i have my doubts about butt "winking" even being an issue. i think it's a case of people noticing "something" and they feel the need to comment on it. and of course, if it's different from what they do, then it must be wrong
i'm flexible enough to where i always touch hamstrings to glutes in squats; i'm pretty sure my hips do the "wink." but guess what? so does this guy's:
the "no no no no" means no belt, straps, knee wraps, and i forget what else. if you read the comments section, he responds to accusations of "butt winking."
i think there is a chance of hurting your back coming out of the "wink" b/c i think the load quickly transfers to your lower back immediately out of the hole (that is, when you squat all the way down). you can avoid this by consciously tightening your glutes throughout the entire squat. i've found that doing so helps protect my lower back going in and out of the hole, and the "wink" doesn't affect my lift at all.
but definitely listen to Fazc, and i hope Fazc will set me straight if i've said anything ignorant.