Theres not alot to go on from the unified rules (section 15 Fouls) : Commonsense tells me that it right to relax the hold (if not release it completely) when the opponent taps whether or not the referee jumps in. To keep going when an opponent taps is unsportsmanlike conduct. Chokes in all likelyhood would not end someones career but leglocks are dangerous in that matter. Should the UFC institute more rules on how to deal with submissions by being more explicit on when holds should be relaxed, possibly deal with leglocks in particular. Possibly rules on video replay decisions and dealing with fake taps. From the above pic, you can see Palhares arms flexing from cranking the submission until the referee jumps in, and the tapping did not make any difference.