The commishions set the rules for what all is oked.........The orgs just set up their rules based on what they like.
Dana in the past has talked about wanting the commishion to allow things like knees to the head when a guy is down, Frank Shamrock said a little while back that he would like elbows on the ground banned and only let guys elbow while standing, Thats what I have wanted for a while I hate ground elbows.
The only thing that would be banned as far as leg locks go is if you did something with their toes.......I think you must control 4 fingers or toes when doing things or it would be considered small joint manipulation and that is not legal.
LoL so you can't grab someones big toe and try to break it off
But for the most part leg locks are just grossly under used in MMA......I've seen way to many fights end by leg lock for guys to still try and make a case that it is to high risk, Take the risk and end the fight........Better then going to the cards !!!!