No, wood mites don't bother snakes- & they live with all sorts of insects in the "real world" too. (You're not talking about using mite spray on these, I hope?) I'd never spray the substrate for mites, just bake it (very low & slow oven), that should kill them off. (Ie. never risk exposing a snake to a toxic substance when a harmless choice will get the job done.) I don't use cypress but I seem to recall many others having this same issue with cypress mulch.