VR (virtual reality not vertical reference) is used in training simulators only, not in the real aircraft, but I believe the Brit Mil are using simulators for USL training as well as winching.
A vertical reference bubble is not much use as you need to be in the door the winchman goes out and comes in so kneeling on the sill directly under the winch is the place to be.
The winchman is the best source of feedback about winch operating technique since he/she is the one being placed into or recovered from the mountain/sea/deck. You could have the best metrics in the world in the sim but if you smash the winchmen into the boat in real life you have completely destroyed your operational capability.
Awareness of the winchman (including his hand signals) his rate of movement vertically and horizontally and a constant scan of the aircraft position and proximity to obstacles are the key elements that need to be trained. That and decent, calm, accurate voice marshalling (patter).
The only practical way to control a spinning stretcher is to either put it back on the ground or get some forward speed on - the best option is to prevent the spin in the first place by using a hi-line or similar.