I appreciate and think I understand your post. In your case, the original installer had connected the HU reverse gear signal wire (violet/white) to the positive lead of the camera. If I read your post correctly and that was the situation, your camera would not have worked for two reasons.
First, your camera was not getting any power. The violet/white reverse gear signal wire at the head unit is an input, not an output. In other words, the violet/white reverse gear signal wire at the HU only has power when it receives it from an external source, i.e. gear shift wire, reverse light. Thus, it cannot power anything. Therefore, the camera would have had to have been rewired, as you stated in your post, to a 12 volt source.
Second, your HU was not receiving a 12 volt load on the reverse gear signal (violet/white) wire in order to change the display to the camera. The violet/white reverse gear signal wire is connected to a momentary switch inside the HU that switches the HU to the camera RCA (brown in the case of the 8000, 7000 and 6000NEX') when it receives a 12 volt load. As soon as the load is removed, the display switches back to normal. In other words, your camera may have power because your key is in the acc. position, but you won't see anything it sees until something tells the HU to switch over to the camera RCA. Plus, you only want it to do it at the right time. For instance, you wouldn't want to connect the violet/white wire of the head unit to the horn because the only time the HU would switch over to the camera RCA is when you push the horn on your steering wheel. While funny, that setup is not very practical or safe. Thus, the person rewiring your camera circuit also rewired your violet/white reverse gear signal wire at your HU to a wire that only has 12 volts when your vehicle's transmission is placed into reverse gear.
I am requesting an RMA from the seller as I believe my problem is not in the wiring outside of the HU. However, I am willing to listen to all ideas.