Depends on the school. Some require a DO letter, some just want a physician but recommend a DO.
Why not get both and send both to the schools? I had a letter from both a DO and an MD. There were several schools I sent both. Even though I knew what was in the MD letter, and it was not great, and did not know what was in the DO letter. They got me acceptances at 3/5 of my first interviews, and I canceled all the interviews that I had scheduled later. Not bad.
dsoz