Since I've dug myself a hole on this I'll might as well dig deeper...
Caster & self-centering - the more caster you have the "higher" the car lifts itself as you turn the wheel. It's gravity that pulls the front wheels to center since it is in that position that the car's ride height is lowest. A car with zero caster would have zero self-centering.
Side to side weight transfer, as in a corner or slide has no affect on self center since it's the weight of the car on the front wheels that is doing the work to self-center.
As examples, go-karts have a lot of caster, you can see the front end rise as you turn the steering and you feel it in your arms. Most of the open wheel cars I've own have had little caster, thus as a driver you have to steering the car straight on corner exit and can't rely on "self-centering" since there's little caster.
IMHO a driver should retain a hold of the steering even in a slide with reverse lock on the steering. This allows the driver to "know" which way the front wheels are pointed at all times.
My fear is that if you release the steering wheel then, how would you know when to grab it again and would you know where the wheels are pointed? In the right direction?
The other thing that can happen, especially in a race, is that you get tagged while trying to recover, which could set the car going in some unpredictable direction. If your hands are off the wheel you've got ZERO chance of recovery.
The only reason I can think of that it's suggested to release the steering wheel at the onset of oversteer is because an inexperienced driver is likely to over correct by inputing too much steering lock. Potentially that's worse, a car may come around in the opposite direction and then there's likely spin.
Okay... deep hole is dug...
Kiyoshi