There is no rule against carrying a portable winch (or even having a fitted on car version fot that matter)... only the (percieved) weight penalty of having one (and a dual battery system to power it... if in the situation (often) that the engine is not running to provide the current.
but often it is deemed quicker/easier to use tow straps/snatch strap to right a vehicle via assistance from another competitor (one of advantages to running in a multi car team).
I've often seen "roofed" cars righted in the sand (not unlike RG's stack) using a combination of belly wrapping the car with a tow strap, and burying the spare wheels as a block/ground anchor point - this prevents th car from just sliding along the sand on the roof). With a bit of muscle (get it on the side) and a gentle tug from another car/or two... often you can have the car back on all four without too much drama (it requires someone to stop and assist for four/five minutes though... provided you have everythiing ready to go... not sitting on the satellite phone relating you predicament to someone who could give a f5%&!
Or you can alwways wait for the T4 trucks toa rrive on the scene... they're used to righting all kinds of f5¤% ups in the dunes!