If it isn't allowed it certainly happens.
As a side note, for me, watching a model sucking on a bong has zero appeal, sexual or otherwise. This may have more to do that in so many rooms where the model is smoking, the chat seems to be an endless stream of idiots talking about weed and how great it is or how wasted they got/get. (For so many Australian models I have seen, it seems to be their only on-cam activity)
And of course, this is their choice, and I move on to other rooms.
