It is possible that mites that infest rats may be the transmission vector for IBD so no mite, either from snake or rat, is ever 'okay'. If you believe you have rat mites, I would suggest changing your supplier. This is a great scholarly resource for those looking to learn more about IBD and its possible transmission vectors. It is an open access articles so it's free for non-subscribers.

Stenglein MD, et al. 2012. Identification, characterization, and in vitro culture of highly divergent arenaviruses from boa constrictors and annulated tree boas: candidate etiological agents for snake inclusion body disease. mBio 3(4):e00180-12.