That cannot be illegal that would be pathetic, what if I had a fat man in my passenger seat? I can still see in the rear view and I can see forward, I didn't check if I can see my side mirror or not, but not all cars even have a right side mirror so I don't think they are required by law.
I see no difference than if I had a pickup truck with a cap filled with junk, or a moving van with no review mirror at all.