The back end is purely driven by an electric motor, if you aren't heavily accelerating or have slip on the front wheels then there will be no power applied to the rear wheels. If you are lightly braking then the electric motor is providing that braking force which is less likely to lock the wheels than the mechanical brakes and the ABS and VSC systems would stop any wheel spin from occurring within a very short space of time.
I never really drove my 400h in that much snow, the one time I did it when up a hill without any issue, a hill that a lot of other cars were struggling with.
The RX300 isn't exactly an off-road vehicle, I'd say the 400h is just as good.