On my Toyota Camry Hybrid the camera is not completely blocked but is next to useless.The rear parking assist constantly beeps and if not shut off it will actually stop my car from reversing. This is one of the reasons I won't keep the rack on my car all the time. The Cross Traffic sensors are fine.
The rack goes on the car, I then shut off Parking Assist and drive away. Of course there is the issue of a blocked licence plate that rarely gets mentioned. 1UP is one of the few racks that address this problem. Depending on your jurisdiction and the mood of the law enforcement officer who pulled you over you may or may not get a citation.
These are the small details that the people at the rack store never tell you. Still love my rack even with these medium sized quibbles.