I may as well tell you my best guesses: I once consulted a slang dictionary and the closest finds were candy = penis (or sex in general); salt = money. From this I extrapolate: candy man = male sexual partner and salty dog = breadwinner. So the song is about the exchange of sexual favors for money, which is certainly plausible, and about setting up a permanent relationship, as opposed to a one-night stand.

Problem #1: Since gay themes are unknown (to me anyway) in folk music, this implies the speaker is a woman, but I have never known the song to be sung by a woman, and it contains no other clues that the story is told from a woman's point of view, which seems strange.

Problem #2: There is another song, "Salty Dog Blues," that goes, "If I can't be your salty dog, then I won't be your man at all. Honey, let me be your salty dog." Why would a man plead with a woman for her to accept his money, when she seems willing to accept him without it?

It turns out both songs are in DigiTrad, and "Candy Man" contains some unhelpful comments (IMHO) about the meaning of the terms.