That's what I was saying. There is a lot that could go wrong (if not done properly). For example, if the ginmal controller and motors pull too much power from the wrong place (Ex: NAZA flight controller or even main board) they could cause a failure or malfunction. Another concern is the noise that motors feedback into the power line (or noise that comes from the P2V to the gimbal), that noise (if not filtered / corrected) could cause problems with the NAZA flight controller or other parts like the GPS, ESC's, radios, ... If you use a separate power source (as it seems they have chosen to do) none of this is any concern, much easier to deal with something when you don't have to think about it.
Simple solution would be to tap into the back of the main battery terminals, use a voltage regulator to step the voltage to what the gimbal requires, wrap the wires four or five times through a ferrite core (just to be safe) and go flying.
EDIT: I just read a little slower, they say "3s" so if you tap into the P2V battery terminal you do not need a voltage regulator, just ferrite core (optional but a good idea) and go. Not too bad, just be careful to not mess up the main lines into the P2V (bad news.)
