Snake mites will NOT be found on rodents. Mites that infest rodents will be a completely different species from those that infest reptiles, and they will not transfer between them.

If there are snake mites in the pet store, you are more likely to bring them home on dry goods, where they may wander into your cages. (I wound up with a minor, mysterious mite outbreak last year, and have to assume that's how it happened--I breed my own rodents). I keep a can of PAM on hand for such potentials.

So, do not treat, spray, or worry about the feeder rodents bringing in mites to your snakes. They won't. A snake mite that wandered onto a rodent would wander right back off of it again, at the same pace.