I know that my advice is similar to everyone else's, but just make sure that the individual knows you very well and can assess your abilities in a number of situations! MSUCOM is very lenient in the way that they accept letters from almost anyone (meaning that they do not need to be a professor, a doctor, or any other type of professional). If you worked closely with an academic adviser, they are very good resources as well and probably have experience writing quality letters. I'm sure that a letter from a D.O. would help, but many people have not had one readily available and neither did I. I received a seat, so it didn't hurt me. 🙂 I wish you the best of luck!
Julia