"If he taps, its Jiu Jitsu" - Rodrigo Gracie
"Here, in the street, in competition, a man confronts you he is the enemy. An enemy deserves no mercy." - Sensei John Kreese
Rodrigo Gracie was doing a seminar at my old gym and rolled with some of the blue belts afterwards.
He taps out one of the blue belts by crunches the guys face into his (sweaty) chest, not as a crank but to suffocate him. It looking like when a guy puts a pillow on someone to kill him.
I thought that was uncalled for, hes a blackbelt so he should be able to get more traditional submissions without having to resort to something like that. The blue belt was much smaller than him but does have an irritating flexible guard.
I don't think that all submissions in class are game. Some submissions are too dangerous or just foster bad habits (such as not trying to pass guard) for regular training.