There are a couple of different things to look at.
#1 Wood Mite - harmless to your snake nothing to worry about
#2 Rat Mite - I have no experience with these but I've been told that they can prey on reptiles for a short period of time during their life cycle so it is possible to have rat mites.
#3 Snake Mite - These don't just show up, they come for bringing in snakes with them on them and not observing proper quarantine or taking your snake out to places where reptile mites might be prone to be found, i.e reptile shows, petco, petsmart, friends house who also keeps reptiles. Also allowing people who keep snakes or other reptiles to handle your animals without first washing their hands or using some kind of cleaner.
Regardless of the type you have I do the same thing with all my animals use some kind of topical like Reptile Relief (as directed) and then Provent-a-Mite (aka "PAM" not the cooking spray) on all bedding, hides, tub or tank, and for a foot or two around the enclosure. If in a rack treating the rack itself is key other wise they will just keep coming back.
Also treat every reptile you own, the odds that you've not cross contaminated them is slim, so better safe than sorry.