Can't say I've ever seen a shop just hang rear sensors only on an AWD vehicle with IRS. Rears have to be aligned to the fronts. They would still have to hang all 4 sensors, but would only adjust for rear toe as that is all they are getting paid for.
Anyway, I suppose anything is possible as most dealers and mechanics like to half ass anything they possibly can. It wouldn't surprise me if some mechanics/dealers are just measuring the links they remove, setting the new ones to the same length, and not actually doing the alignment. More money in their pocket that way, plus they turn the vehicle quicker.