A hot dog can be a type of sausage in which case it is an ingredient. A package of raw hot dogs in the refrigerator is not a dish.
A hot dog can also be one of those sausages on a bun with some condiments and/or vegetables (mustard, onions, pickles) in which case it is technically a dish. However, I doubt that anyone would casually refer to it that way.
I don't think I ever hear dish used in the sense of #2 except
- in discussions on WordReference and
- among people who are not native speakers of English and
- in the rhyme Sing a Song of Sixpence, and that is about blackbird pie, not hot-dogs. The words are shown and the poem is discussed here: http://en.wikipedia.org/wiki/Sing_a_Song_of_Sixpence
I agree with ewie and se16. In theory, anything you eat could be a 'dish.' In practice, it's those things that are served in dishes, on plates, in bowls.
As Myr points out, too. The phrase 'hot dog' has two senses, either the sausage or the whole combo; but neither is really a 'dish'. The latter [in usage] is similar to a ham sandwich. If you are served one, you probably do NOT say, "What a tasty dish!"
"Dish" can also mean a course in a meal with multiple courses:
The first dish served was Oysters Rockefeller. This was followed by a dish featuring couscous and quail eggs. The next dish was a kosher hot dog served in sauce Perigourdine with truffles, and that was followed by the main course of roasted free-range yak with apple butter and rutabagas.