This is a standard Martin Chambers move. I read an article about him in Modern Drummer a few years ago and he said he pours water on the floors at random for effect. The really wild part is that he has to wrap all of his SM 57s with non-lubed condoms to protect them from the overspray. Apparently they are thin enough to avoid altering the sound.
If the bearing edges or inside of a wood drum gets wet and the water sits on it for a while, I'm sure it'd cause some damage. The biggest danger would be rusting your hardware. You'd have to disassemble the shells and hardware to make sure you dried everything out, afterward. Seems like a big hassle for a gimmick.
I was watching a Pretenders live special last night, and whenever Martin Chambers would hit the low floor tom, water would splash into the air. Im guessing he just pours some on it at the beginning of the show. Do you think this would this damage the head or drum in anyway? Has anyone else heard of this craziness before??