Generally, having tires on a car at those temps may damage the tire where it is flexed at the contact points. Generally, if the tires are on rims and not on a car (no deformity of the tire)freezing should not have damaged the tire at all.
Generally, even if the tire is on a car and on the ground, if it is warmed up prior to moving the car, it should be OK as well.
In fact, you have proably improved their performance and life due to the slow, controlled curing of the tires. I think that is an unfair advantage and those tires should be illegal.
Joe, I think you should rule that they are just wrong and take away 2 races of points and put him in the back at the Nationals.
Big Dog