People keep bringing it up as some sort of theoretical bogeyman, doesn't mean there's any substance to it. I don't know how any of us could shoot it down beyond asking for some sort of proof that it's ever happened, or that there is a mechanism in place to make this happen, or anything along those lines...people keep repeating this
The only official stance I know of is what I was told by my GUE instructor during the only course I have taken, and it was the usual/expected/reasonable "we teach our system, what you do afterwards is your business, take it or leave it" like any other agency.
GUE Instructors are expected to behave as positive examples for GUE, and there are defined repercussions for when they don't, such as losing their instructor status. I think things are much the same in that regard in other agencies.