In terms of definition, The hot dog is a sandwich, Especially in the United States where many federal agencies have definitions of sandwiches which include hotdogs(for tax purposes). They can not be a taco as tacos are made with tortillas and hot dogs obviously use bread. The definition of a hotdog fits closer with a sandwich than a taco.
A hot dog is a sausage in a bun with or without extra fillings,
A taco is a tortilla with filling on top
A torta is a mexican sandwitch
A hot dog is more akin to a torta than taco, But it still would not even count as a torta.
Know your difference or Gorden Ramsey will curse at you and call you a #$@%% sandwich.
It is a U shaped vessel filled with meat and other potential toppings. How can it be anything else but a taco? Sandwiches require two separated sides to contain the filling. But Tacos are one container that wraps around the filling with one side opened. That's all I have to say.