I'm not a mite expert but I don't think you need to worry. I know there are "wood mites" too, but they don't bother snakes, so I don't think soil mites will either.
Snake mites live by sucking snake blood...other kinds of mites don't do that, they're just going to be harmless 'room-mates' as far as I know, though I have no
experience with bioactive tanks, if there's anything else they might have an impact on?