Memphis,
As far as I know, the term "Salty Dog" is an old term for a seasoned sailor. In doing a little research on the Morris Brothers' song, I fould a couple of explanations. The most plausible seems that they wrote it after frequenting either a restaurant or a "honky-tonk" somewhere in North Carolina. Apparently, there was also a snack food back in the 30's called "Salty Dog," but I can't find much info on that.