OK, so not having seen your situation (some inspections legally require that the inspector touch the materials!), please know that I can only really provide general information. Roofing materials and ceiling materials are not the same. So, if I understand what you have said, the asbestos is present in the roofing materials, as in, the exterior? You would be screwing the polemount into an exposed wooden beam from the interior (and not all the way through the beam)?
Just generally based off this information without having seen the actual situation firsthand, this does not sound like a problem. Typically, the exposed beam on the interior would not be in contact with the asbestos roofing materials, as the roofing is likely laid on a plywood decking, laid over the ceiling beams. There are many types of asbestos roofing materials, from the nicollete paper to roofing tar, so I cannot tell you any specifics, because I do not know about your particular roofing system. However, if you are permanently mounting a pole on a beam, there should be no movement of said beam at all. I would not think this situation, as I understand it, would be a problem for the roofing materials, assuming roofing and beam you want to use are in good shape, not leaking, rotten, falling in, etc.