Concerns/Considerations for making mead with raw honey?

Well, I'm a microbiologist and brewer. Bacteria will not GROW in pure Honey but they can survive. When honey is diluted to make mead it's party time for bacteria! Heating honey by boiling may kill some bacteria but spores can survive (including Clostridium). To kill spores you need a temperature of 121C sustained for a minimum of 20 minutes. This is typically accomplished with steam under pressure as in an autoclave (or pressure cooker). Boiling will obviously blow off volatile flavour components but will not by any means toxify the honey. I'm not saying that making mead with raw honey with a heavy dose of yeast (to overwhelm bacteria) is going to kill you. However I'm guessing that if it did kill someone they aren't posting here to warn us!

*Not an expert but...
I believe I have read that Honey is not a great food source for yeast as it doesn't have ample levels of all the bits and pieces needed to make happy baby yeasties. So your recipe may need some nutritional source like DAP (yeast nutrients) or fruits for flavoured meads (melomel).

Re: HONEY SHOULD NEVER BE HEATED AT ALL.
(Sorry apparently I need 50Rep to sub-comment???)

Wikipedia says

In humans, no correlation between intakes of HMF and disease is known.

I'm not sure how dangerous heated honey is, but apparently coffee contains more of 'it'. So your yearly intake of coffee vs yearly intake of mead? I'd say mead is good to drink!

fresh honey contains less than 15 mg/kg—depending on pH-value and temperature and age,[11] and the codex alimentarius standard requires that honey have less than 40 mg/kg HMf to guarantee that the honey has not undergone heating during processing, except for tropical honeys which must be below 80 mg/kg.

Several types of roasted coffee contained between 300 – 2900 mg/kg HMF.

HONEY SHOULD NEVER BE HEATED AT ALL. I have myself seen this poisonous effect on one of my relatives who used to take honey in hot fluids. this affected him badly. when he went to the doctor, and after months of diagnosis, he was diagnosed with the accumulation of a glue like substance in his body, and very late it was discovered that this was due to the heated honey. the heating of honey changes the molecular structure of the honey and makes it highly toxic. it should be made compulsory by all the legislations in the world to mark on the bottles that honey should not be heated. also, it is a shame that too many companies these days are marketing their cereals with honey, whose preparation involves heating the cereals to cook them. the right procedure is only to cook the cerals, then make them luke warm and thereafter only add honey. these companies who are marketing so many sorts of “processed foods” as “healthy choices for people” should be banned by people, as no government around the world have hands big enough to ban these big and powerful brands. this has been scientifically proven that when honey is heated, it forms a chemical called as hydroxymethyl furfuraldehyde (HMF) and also chemically alters its basic structure/ composition while increasing peroxides.

I was going to point out that organisms that produce endospores, like Clostridium botulinum survive in honey, but then I remembered that you can not kill them by boiling. The spores could also be naturally present in anything you brew or preserve. This is why you should use a pressure cooker for canning non-acidic foods.

I did a bit more research, and found this:

Various bacteria have been inoculated into aseptically collected honey held at 20°C. The result showed loss of bacterial viability within 8–24 days. It is only the spore forming microorganisms that can survive in honey at low temperature.

Honey: a reservoir for microorganisms and an inhibitory agent for microbes, Olatien et.al

Bacterial endospores live four hours in boiling heat, UV, and pretty much everything else.

Anything you can kill without a pressure cooker, autoclave or gamma radiation is dead after a couple of weeks in honey at room temperature.

People will tell you that bugs won't grow in raw honey, and they're right. The bad news is that they're still there and they'll grow just fine when you add water to make the must. (Let's remember people, there are bee parts in this stuff...)

If you pitch well with a very large yeast population, it is possible to have a fine ferment and a fine mead because of population pressure (large populations can cooperatively out-compete other bugs). This can be preferable because you won't lose your aromatics due to volatilization during heat pasteurization.

On the other hand, if you're unsure about your pitch or you don't like to take risks you can also sterilize your must following standard techniques (plenty of which are suggested here in other answers, or in easy to find online resources). It's also worth noting that a heat process can also help produce a clearer mead (I'm guessing due to denatured proteins), but it's not strictly necessary for a crystal clear mead.

Addendum:

I've always used raw honey, but I've had mild infections that are producing off-flavors in my mead. I'm currently looking into processes that will let me have the best of both worlds. My next experiments will be: - Long term (6+ hours) closed bottle pasteurization of my honey at low temperatures. - UV sterilization of must (utilizing an unfiltered UV light source and an even longer time).

Most micro organisms will not grow in honey due to it's low water activity rating of 0.6. Bacteria needs at least 0.91 and fungi needs .7 water activity to grow. The water activity of distilled water is exactly 1. Most honey should be fine for making mead without heating. You do need to be aware that if it starts to separate the water activity has changed due to outside moisture and it may be able to support bacteria. I have made many meads and have never heated or used campden tablets without any infections. As long as your fermentation is strong and healthy you shouldn't have any problems with bacteria from raw honey.

In the words of Dwight Schrute, "That's debatable. There are basically two schools of thought..."

Some people swear that honey should never be heated, and others maintain that heating or chemical pasteurization is necessary. Regardless of your stance, it's undeniable that heating honey destroys it's aroma and flavor, so it's best to minimize the amount of heat added. Heating up to 37°C (98.6° F) causes loss of nearly 200 components, some of which are antibacterial. Heating up to 40°C (104° F) destroys invertase, an important enzyme. At 50°C (122° F), the honey sugars caramelize.

If you do heat, you can follow this pasteurization table:

Temperature    Time (min)
123°F / 51°C             470
130°F / 55°C             170
135°F / 57°C             60
140°F / 60°C             22
145°F / 63°C             7.5

Do not heat pure honey, as it is difficult to keep it evenly mixed and at a uniform temperature. Instead, mix it with warm water.

If you choose not to heat, you can add metabisulfate (Campden) if you're still nervous about wild yeast or bacteria in the honey. However, many homebrewers don't pasteurize or add Campden to their honey, particularly when making meads and braggots. Because honey is hydrophilic, most bugs can't grow in it, so the risk of contamination is low.