Why don't you do this:
Call the person - don't write or email them... call them - who offered you "admission" into the MSAP at SGU. Tell them that you have an admission directly into Ross University's MD program (i.e., not their MERP or anything else).
See what they say. I would imagine it will be something like, "Well, we can't make that decision for you." (etc.)
If you don't hear what you think you should hear, respond to that person exactly this: "Well, I would really prefer instead to enroll directly into SGU's MD program and not do the MSAP." (*NB: If that's what you want to do.)
You will get the answer you need to hear. Otherwise, no one here has the information you're asking. The school does. They may share it with you. But, no way to verify what they tell you.
-Skip