I can speak for FLL's T1 and T2 - there is either an ID or 'status' checker at the head of the line entrance to make sure people go into the correct lane, always at T2 and at T1 during busy periods. At FLL, I have seen elite line interlopers tossed out and sent back to the end of the regular line by the ID checkers, and I have had to remove some jetBlue people myself from the CO/NW elite line there as well.