Not really a spacer, the rack is designed for disc brakes so it has a thick L-tab as you can see on this picture, the black L shaped piece is the bottom of the rack, this is the "inside" view across the frame with the wheel removed:
It's better than a plain spacer, since it's rigid and has larger contact surface but still not ideal. The issue you mentioned still exists to some degree. That's one more reason to go Big Dummy
Yes, he did this to both of them. I wanted them improved not just fixed and he agreed that the other one was just waiting to be broken off