The winch would pull down the one battery too far if hooked to one of the power drive batteries. Then other issues would emerge such as uneven charging etc., etc.
I recommend installing the OEM optional winch battery kit that comes with the proper wiring harness, tray hold down and 2 12v AGM batteries. (Note the kit is year specific).
The only problem I have found is that the winch batteries are not connected to charge while the unit is plugged in. The winch batteries charge while the vehicle is moving under regenerative braking. This is not really a problem unless you start using the winch a lot and/or hook other things up to them such as aux. lights. In such case there are 2 solutions to add more charging to the winch batteries:
1. Jury rig a 12v inverter into the 110v charger input which would allow direct plug in charging of the winch batteries.
2. Install a Battery Minder SCC-015 12v, 15 watt solar battery charger/maintainer/desulfator.
NOTE: in a pinch you can use an automotive battery charger to charge both winch batteries.....just connect + to + on driver's side battery and - to - on passenger side battery (winch batteries are connected in parallel).