Was the last play in The Longest Yard(2005) completely fair?

Only certain types of deception or misdirection are prohibited in football; specifically, anything that simulates a snap or the beginning of a play is prohibited (so a center making jerking movements, a back starting to run forward, etc.). The talking, slow standing, moving backward, etc. is all allowed.

Having said that, there is another rule that states that those on the line (and there must be at least 6 when the ball is snapped) must be completely set at least 1 second before the snap. Notice when Crewe is heading over to talk to Scarborough ... several linemen stand up. This is legal, but if they don't either A) get back down in their stances for at least one second, or B) stay perfectly still for at least one second, then they would be penalized. The last view we see is of Crewe, and then the ball is snapped, so we never see what the linemen do.

To sum everything up, it is certainly plausible as a legal play, but the camera angles make it impossible to confirm or deny whether it was executed legally.

EDIT (to address rest of question): Nothing throughout the rest of the movie really sticks out in my mind as being obviously illegal or implausible, although admittedly it's been 4 or 5 years since I watched the whole thing ... I refreshed my memory on Netflix of those final scenes last night. One thing to note about the final scoring play (before the two-point conversion); while the Fumblerooski is a perfectly legal play in pro football most of the time (it was banned in college football in 1992), a while ago the pro rules were changed that outlaw it in the final two minutes of either half or when it's fourth down (in those situations, the rule now states that an offensive player can only advance a fumbled ball if he is the one who fumbled it). I don't believe that rule was in effect at the time the movie was made, however, so we'd have to assume the game was being played under pro rules (or some form of house rules).