Looking through all of the posts I realize that I did not address the OP's original question about the sponsor. Personally, I think that a potential sponsor has an absolute right to choose who to sponsor. If the sponsee's behavior does not align with the sponsor's view of sobriety then the sponsor should be free to choose not to sponsor that person.
I'm may complicate things a bit here but here goes. I do not buy into the "if it's prescribed by a doctor it's OK" concept. I think in many cases the whole prescribed marijuana concept is a hoax. I know a person who shopped doctors to get Xanax. So it was prescribed. But IMO not needed. I would never consider sponsoring him. Additionally, I would not sponsor someone who smokes/uses tobacco either. But that's just me. I'm not suggesting that I am "right" about my approach to sponsorship but that's how I feel today. YMMV.