I am currently a OMS-II and also am intersted in derm. It is true that there are only a few, I want to say 6 derm D.O. residencies in the whole country, but there is hope! I know 2 people from CCOM that matched in derm this year. No matter which you decide to go into D.O. or M.D. it is about who you know and how are you really want to do derm. Many M.D. programs are becoming more accustomed to D.O. students and are realizing that our knowledge base is just as strong as M.D. students.
It is often said that D.O.'s are more personable (I promise I am not M.D. bashing)-so I personally feel that an M.D. program would rather have a hard working, passionate D.O. with a great personality over a hard working M.D. without any social skills. In the end it is the residence who interview you, and if you are someone that they would like to work with then hopefully it won't make a difference if you are an M.D. or D.O. At least this is the motto that I am working with
Good luck!