Oh gosh, I don't know. I didn't think they were allowed to accept tips either. We took the Walk in Walt's Footsteps tour last February. At the end of our tour, I saw another member in our tour group tip the guide. I was surprised when the CM accepted it, and my feelings towards her were kind of tainted after that. (I had to keep telling myself that she was probably turning it in after we all left.) If tipping is allowed, now I feel a little guilty about not tipping her myself!
It will be interesting to hear if someone knows for sure.