I've never gotten mites from aspen bedding and I use it in all of my tubs, but it is possible for there to be some in the bedding. What I usually do is if I don't trust something and suspect there may be mites, I do a mite treatment just to be safe.

If you're worried about it, treating the bedding doesn't hurt, but I'd be more inclined to believe that the mites in your aspen bedding was more of a freak occurance than anything, usually it's fine.