Hot dogs are definitley high in sodium, but - it won't hurt your puppy if they're few and far between. I generally try to remember the general rule "high in protien, low in salt" for the human food treats I feed my gang and even for some of your average packaged treats made specifically for dogs. What about some hard boiled egg, not the yolk but the whites, cut also into cubes like the cheese? Again, you'll have to try these out and see what your puppy likes, but if he's interested in salmon, he may also like the taste of the egg.
(And of course my favorite treat, lavish with affection and praise!! It's low in fat,calories, and doesn't cost anything! heehee! Okay, yes, I'm cheesie.)