Reptile Relief can be applied directly to the snake. I hate the stuff, because of the smell. I think it reeks, but that's me. In any case, I've used it on a few severly infested animals I picked up from Craiglist before I brought them into the house. I then also treated their enclosures with PAM and the mite problem was gone.
Yes, if you get the PAM, treat the enclosure and put the snake back in, it will kill the mites that are on him - you do NOT have to treat in conjunction with Reptile Relief.