[BMERDOC]

To answer your question, no, there is no way to check rotor balance. If you can't feel a direct vibration in the steering wheel then you are correct to assume that the vibration is coming from the rear. If its a pulsing vibration I would consider looking more into a driveline vibration like a bad u-joint or an driveshaft that is tweaked or needs a rebalance. Is the driveshaft a one piece or two? If its a two piece then the center bearing could be to blame also. I wish you luck in finding your problem.