I wouldn't have thought so. There were "yellow dog Democrats" long, long, long before there were "blue dog" Democrat politicians.
Anyone from the South would have understood immediately.
Well then, not being from the south I'll just quit the thread.
You are right. Yellow Dog and Blue Dog are not the same. Blue Dogs took that nickname to differentiate themselves from the liberal Democrats in the party. In my opinion, it is used to “fool” the old time dems (and yellow dogs) AND keep conservatives voting for them, thereby preventing them from supporting Republicans. I don’t know what “Blue” means though.