The problem with 'supply noise' on the camera supply input COULD cause the issues that are described. It would very much depend on the camera module, how well it's made etc etc... the idea of the 2nd relay is that it will provide a clean switched +ve supply to the camera that doesn't also have the reversing light bulbs/LEDs on the same circuit.

It could be done with a single relay that has two sets of changeover/switching contacts so the coil is energised from the reversing light cct, one set of contacts is used to ground pin 17, the other set of contacts is used to switch 12v to the camera supply.

Personally, I'd go for a single relay with the two sets of contacts if you can source one.