Yes he(she) did Phil
2013 GD2 Trophy.
I'm not familiar what they fit into the Trophy as a head unit, but if it can't play back DVDs or video in some form, it won't have the hardware to act as a rearview monitor.
Rear cameras don't normally use AUX input, the head units have a dedicated input that is switched by the reverse lights coming on, so it's fully automatic and it works when the unit is turned off too.
If the Trophy unit can display video, you could always pull it out from the dash and see if it has any video/AV in. If it does, something can be done to make use of a rearview cam.
You can search for the thread I did about my changeover and all the camera related experiences, but I changed the head unit in my FD. Most of the other info should be relevant for the GD too.