What I would be worried about most is the mounting points on the car where the hitch mounts. I suspect that most of the damage will be at those locations. Though, depending on how it mounts, it is probably just stretching holes, but it could be worse like separated seems.
Although, theoretically, 150 lbs of bikes is 150 lbs of bikes, whether 2 ft. from the hitch or 20 ft. from the hitch, the way the load is distributed on the cars' mounting points drastically changes.
I have seen hitched that mount mostly to sheet metal parts (like the bitch for my car--two holes are drilled into the sheet metal of the spare tire well, and two bolts hold steel plates on both sides of the sheet metal.) bend panels and even separate the whole panel at the seems (keep in mind that a panel like a spare tire well is usually only spot welded and the seam is covered with seam sealer. Some seams on some newer cars are only bonded with adhesives).
If it mounts to the sub-frame (or a factory reinforced part of the uni-body), I wouldn't worry too much about having 125 lbs of bikes on there. Even if you do damage, it will probably be minor enough that you'll never notice (unless you go to remove the hitch).