A framebuilder friend described to me an incident where one of his customers changed a flat tire. While doing so, he put the chain on the chain hanger that was brazed to the right seat stay. Unfortunately, he forgot to move the chain back to the freewheel/cogset before trying to ride off. The chain hanger remained fixed to the seat stay, however the seat stay was twisted into a nasty shape that required the attention of said framebuilder. In other words, if brazed correctly, a rack would be fine.