They do close accounts or penalize them if they can prove it…but if they are in the same house that is hard to do. Mostly that comes into play when there is some sort of CS issue. If someone tries to appeal an account action by saying “but my GF did it”, then that won’t be accepted. If someone tries to take control of an account and their name is not on the account, Blizz won’t allow it. Anything that requires proof someone is the account holder goes to the name on the account.
This is normally how account sharing is proven. Blizzard does have that information although there are ways to make it harder for Blizzard to tell. I have only seen actions against accounts in WoW, but the policy is the same across games should they enforce it.
I don’t think they take donations… I suppose you could argue him playing D4 is a marketing or advertising contribution but that is not really the same thing.
I think Blizzard would just be aware of the backlash if he got banned - even if he deserves it. He gets a lot of media attention and can direct a lot of negative press at any person or group he wants. The mob that follows can be unpleasant for anyone to deal with.
Blizzard is inconsistent on enforcement without even talking about the famous person. Some exploits they take care of, others they let slide. Some people get harshly penalized, others do not. This is esp true in the Diablo games. They do botting/automation ban waves at times, but that seems to be most of it.