It all depends what camera you want.
Some of the cameras from VW use composite video (like a cable TV connection) this is because VW uses different manufacturers. The Camera for the Golf, the one that flips out all cool, uses component or RGBS which is 4 separate wires.
Depending on what type of video input your unit allows, it can be done. The power and control is all done via wiring separate from the head unit.
If your unit does not accept the right video feed to support the OEM camera, they do make converters that can do this.
Again, it all depends on which camera you want to use and what kind of video your head unit accepts.