Just a warning, many program directors would rather have you do a prelim year of internal medicine. I've had many PDs directly ask me that question while on the interview trail. On top of that, I've had residents tell me to make sure I'm not doing a "cush" prelim year because I will feel unprepared for the acute problems in rehab these days.
PM&R programs with their own PGY-1 year are few and far between. The reason is due to the funding required to pay residents that won't even be working in their department for a whole year. However, from residents I've talked to, it seems to make life a lot easier if you've done your first year at the same institution. You'll know the people and the system. So if there's a seperate prelim medicine or TY available at the rehab program, go ahead and apply for it.
