RE: Ketchup on a hot dog
There is a famous, well at least in Lewistown, Pa. they are famous, hotdog shop called Laskaris's. Haven't been there in years, but I know they are still there. Not sure about the brand of dog used, but the buns are steamed, the dogs grilled on a grill that's been there for well over 50 years, they come with mustard, meat sauce, and raw onion.
These are the only dogs I put a bit of ketchup on, it just tastes good with the mustard, sauce and onions.
Other then that I never use ketchup on a hotdog, but I don't see a problem with using it.