Your friend should be able to drive now if his license is valid and filing the SR22 was the only thing required of him by law to start driving again. He should be covered to drive other cars as long as the car owner's insurance company does not have an exclusion or issue about it.

The SR-22 provides liability coverage only so it would not cover any physical damage to the vehicle he is driving. The owner of the vehicle that he is driving would be the primary insurance coverage on the vehicle.