Ankle locks are as legit as they come, and are all over the place at the highest level of submission wrestling. Some people are just not prepared for them and I bet many academies with varying levels of skill spend not enough time training with them.
I like nogi for this. We spend a week a month training without the GI and include all foot attacks. For dangerous ones like heel hooks, we just use these as a catch position and don't twist. That way nobody gets hurt but even the beginners can play.
Collect feet all day long and ignore the sore losers.
Right on man, we do the same with the catch and release. But you know you always have some new guy who comes in and things he is going to be the next GSP and looks to crank every sub they catch, this could be a huge problem with a Heel Hook. I agree collect them and forget them.