What makes it "safe" for Auto-X is that you're less-likely to roll the car than you are on a racetrack. I'm not sure I really buy that logic (I mean, how likely are you to roll a car *ever*? Either you ignore the low-probability danger or you don't).
Regardless of how you feel about all that (all safety is a tradeoff after all - you'd be safer not driving at all!), if you're going 4-point instead of 5/6-point, consider using Scroth's belts with the anti-submarining feature, e.g.
SCHROTH RACING > Professional Racing Harnesses . It helps make up for the lack of 5/6-point attachment by letting your shoulder roll forward a bit to keep you from digging under the lap belt and getting really ****** up.