I belive those are aspen mites (I have also heard them called wood mites). Strange though, I have never seen them in my aspen, only cypress.
It's my understanding too that they are harmless to reptiles but they bug me. In the cases where I have found them, I clean the cage thuroughly and dose the new bedding with Provent a Mite. Always takes care of them and they don't seem to reoccur with the frequency of reptile mites. I had a friend who would also bake his cypress in the oven prior to using it. He belived that they would come with it for the store and he used that as a preventative measure before he ever saw any pests.
I have noticed the more wet the cypress the faster they multiply.
Milo