I had a LOR from a MD and a DO, and I got accepted at both NYCOM and PCOM. I would recommend it.
This is what someone told me about having a letter from a DO:
Imagine you are on the adcom of your desired med school, and you have two candidates in front of you, same stats, same EC's, etc. Now one student has a LOR from a DO, and the other applicant doesn't have a letter from a DO. Who would you pick??
It seems feasible to think that the letter from a DO does carry some weight.