As best as I can tell, the park has the best of both worlds, officially it is forbidden to hunt in the park but they allow park licensed guides to kill Pez Leon. Real world they are not enforcing the 'DM' only rule but they always have it their back pocket, if needed. If the visiting hunters get out of hand or begin causing damage to the reef they can shut it off with great fanfare and punitive damage to the operator associated with them. As to which operators blind eye customers hunting, it is a personnel choice by the operator, like rinsing wetsuits, check with them privately.
As it stands the stocks of Lion Fish in the park have plummeted in the last couple years, a good friend was only able to get 9 kills in a 2 tank dive last week. They are there but avoiding the apex predator, divers. Outside the park they are hunted by very capable fisherman with slings.
Last year I read a quote that the Pez Leon population in Cozumel was 1/3 of the average of other areas of the Carib, I personnely think it less than half that now: I am proud of the couple hundred I killed last year (especially the POS that stung me), I would like to see any recent reef survey data posted to this thread or another SB thread.