The standard wisdom I've seen is, as mentioned, that glass and metal "should" be fine but plastic is much more prone to scratching, making it a concern.
Brett has a reputation of being very resilient and being able to survive in small nooks and crannies of your equipment, waiting to infect future batches regardless of how well you may try to sanitize it.
I think it's important to note though that Brett isn't this invincible super fungus. With equipment that is free of scratches, good sanitation practices should take care of it. However, it's hard to guarantee that your equipment is, and stays, scratch free. So most brewers seem to take a don't-risk-it-use-separate-equipment approach.
For what it's worth, I have personally used a plastic bucket to make a sour (using Brett, lactobacillus, and pediococcus) and then turned right around and made a Hefeweizen in the same bucket that came out fine. That said, it is a newer bucket (I've only used it for a handful of batches) and I was careful to clean and sanitize it extremely well.
So you won't necessarily have a problem in the short term if your equipment is in good condition but over time as your risk of scratches increases you may become more vulnerable to "infecting your equipment."