Thank you for all the thoughtful responses. My main concerns are not around a tug-of-war over charts or the legal issues. I am not terribly keen in the idea of requiring staff (who we share) have to log in and out of different user profiles to access two different AC databases.
As pointed out by GNicoll, it looks fairly straight forward to run reports including Meaningful Use reports by physician. So sharing a database looks like the way to go for us. The new doc will be billing under her own Tax ID number though so I will need to make sure that doesn't create a problem. Anyone have any experience with that?