My truck has these big shiny things that hang off the the sides of the doors. When I look in them I can see behind me!
Next thing you're going to tell me is that they now have trucks that shift their own gears! ;-)
I don't know about connecting to existing camera systems since I don't have one, I installed a three camera setup from Rearview Safety (hitch, back of camper, back of trailer) that I've been pretty happy with. The quality of the interconnects and wires was really good, though it should be for the price.