After doing a bit of research, I just received and quickly tested (with some clip leads and the head unit hanging out of the dash) a Rydeen MINy camera using SVXdc's 16 pin harness with the stock 6 volt wire out of the Fujitsu FW602US nav unit in my '12 WRX.
I confirmed with tech support at Rydeen that the camera has an operating range from 3.5 to 15 volts. I suspect other cameras both from Rydeen or other MFGs will work the same way, but I recommend checking with their tech support first.
In my brief test, it works perfectly.
The nice thing about this setup is, the camera doesn't need to be constant powered and there is no splicing into other wires necessary. It also seems that the head unit turns the camera on correctly at boot up. I tried starting the car while in neutral and then shifted into reverse and the camera came right on. Subsequent shifts back and forth worked perfectly too. The MINy has switchable guide lines.
I will do the complete install soon and re-confirm that it still works properly. I will also include some pictures.
The camera I got is the MINy, 1st one, top left of the page
I ordered from one of their authorized distributors for warranty etc., they were within $1US of the cheapest shipped price on eBay when I checked.
The harness and plug came from here.
Make sure you tell Dave, you want the stock power out option if you are going to try this.