kinda of an open question. cupping could be caused by tires being out of balance, worn shocks, or just plain junk tires. feathering could be just a toe adjustment.
is this the first set of tires this happened to? how/where was the frame hit? how bad is the alignment? sometimes the factory spec cause tire wear. I personally just read my tire and adjust accordingly if its excessive.(or tell the guy/girl that is doing the alignment to change it)