I have not yet had much of a rash, but I am a bit of a makeup junkie... I can't speak to the Nicole Paxson but I would highly recommend CoverFX for high coverage (found at Sephora), or the Make Up For Ever high coverage concealer. The first one's a bit easier to work with in my experience.
www.inmykit.com has recommendations from a pro makeup artist; I've found many great products that way.