I think the natural tendency of all us SDNers is to overanalyze every single little aspect of our applications. If the rest of your app is good, I don't think they would really care about the CC recommendation. He knows you, and that's what they want, right? Someone who can really talk about who you are, your performance, and how they think you would be a good dentist. If you know this professor best, I absolutely say go for it!