We have run into several similar situations over the years, which leads me to belive that your processor is on the right track. Whether it was a  result of a car, firearm, bow, or just fighting it sounds like your buck had a gangrenous injury to his rear leg. The smell is most likely the result of the decaying tissue.
    Normally we trim around the injury and discard any noticeably affected tissue. I would use the backstraps for your steaks, the front 1/4's and neck for roasts, and grind the meat from the hindquarters which were most affected.  You would want to use the ground meat in seasoned sausage either fresh or smoked, which will help reduce any noticeable off taste.

Dave & Ruth
D & R Processing