The Green/Black wire at that connector comes comes directly from pin 5 on C361 at the BeCM which is the forward most connector on the side of the BeCM next to the transmission tunnel so a bit of a bugger to get to. The two feeds to the reversing lights themselves are a Light Green/Black at pin 2 on C325 that goes to the LH reversing light and a Green/Black on pin 9 of the same connector which goes to the RH reversing light. C325 is a Grey plug on the front of the BeCM, nearest the outside of the car.
Although getting at C325 is going to be much easier, depending on how much current is going to be drawn may trip the blown bulb warning so it would probably be better coming off C361. A friend has one of those huge motorhomes with reversing camera (angled downwards) as well as a camera to act as a rear view mirror (angled horizontally). As soon as he selects reverse, he gets a warning light on the dash telling him the reversing light bulb is blown as his equivalent to the BeCM is seeing a greater current draw than it expects so assumes the bulb has gone short circuit.