Mites are species-specific, rat mites won't affect your snakes. However, it is possible for snake mites to hitch a ride on the rats, if you feel like it's not likely to carry snake mites, feel free to feed. If you have the means of treating the snakes for mites in the event that snake mites were on the rats, I would feed. In the future, I would probably avoid where you got your rats, mites are not good, regardless.
ETA: Definitely contact the store, and if you're going to freeze them for a few days I think you're most definitely fine to feed them.
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