As a welder I would question the integrity of those welds! they don`t look the best and look as if there is not much penetration into the metal. the other issue is it is not gusseted as someone else mentioned. with as far back as that rack is with 4 bikes on it I would be very concerned about stressing the added on receiver and rack to the point it will tear the metal apart! I have a bolt on receiver on my bumper but it is reinforced, and I added 2 ratcheting straps to it so that it doesn`t bounce up and down which is what fatigues the metal.
I would have to say with looking at that setup that it needs to be reengineered, as in removed and redone.
Sorry!