So far I have had good luck sending and recieving plants. The temps here have been mild lately, I try to watch for mild weather and I wrap them in lots of plastic bags and then newspapers. Hopefully they are sitting in a post office or delivery truck and keeping warm!
If they are still dorment when you send them, the cold shouldn't hurt them at all. Sending house plant cuttings or tropicals would be a different story though. Late last fall I sent houseplant cuttings to Michigan. It was mild weather here, but in Michigan, they got snow. The cuttings might have been ok but the mail person left the box on their porch when he found no one was home. After they got home they found the box buried under snow. Needless to say, the cuttings didn't make it.