In observing an OMS residency, I noticed that the program director posted job listing letters on the cork board in the residents' room. Out of about seven letters on the board, only one indicated specific interest in dual-degree surgeons. It was a multi-specialty group full of other MDs seeking an oral surgeon to do full-scope, including orthognathics and cosmetics.
I have seen other people on this board indicate that the MD might be useful for referrals (that is, MD oral surgeons who believe their MD might have helped them get some referrals---though not in an arrogant way), while others indicate that is not true. In any case, I think the MD would be secondary to your ability to communicate and help the referring dentist understand the case.