Yes, those are to be expected in AGBs. Kinda like the symbiotic mites the Madagascan hissing roaches have, they are harmless and don't seem to stress out their hosts. Grain/soil mites however, are a completely different story.There is a species of mite that is symbiotic with this species of milipede. It lives on the pede and appears to clean between the legs and in all the cracks and crevices. So far these mites do not seem to thrive away from the pede, and pose no risk to other arthropods.
I have yet to see any of the small predatory mites in my enclosure, though it is still very new.