Maybe the reason that it has not been enforced is that a lot of local law enforcement not only frequent these businesses, but also date the entertainers. This is true as well of firemen and city officials who all get in free. In fact, not long ago in a club in Detroit, an off duty police officer lost his gun and could not find it. Another became mad at this girlfriend who was a dancer. Upon leaving, he discharged his gun into the door, hitting the owner of the club in his face.
Violence does occur.
Once during a dancers' meeting, the manager had upset one of the girls who happened to be a member of a gang. She had him beaten up badly following the meeting. Another manager tried to force himself on an entertainer. Again, her boyfriend belonged to a gang and a bomb threat as well as violence occurred at the club. He was not terminated but merely sent to another club.