There is no way I could provide you proof. I am getting this from my own personal experience from playing the game countless times. There's your proof.
EDIT: On top of that, the chances of you coming across one of the enterable interiors is slim. So even if there was anything "dirty" inside the club, you would never come across it. Most of your time in GTA: TBoGT Multiplayer will be spent on the streets and such.