I guess the point is, why use hot dogs when there are so many other cheap things you could use? I disagree that bad stuff is not bad for you as long as you eat some good stuff along with it. If you want to eat 4 strips of bacon, putting the 4 strips of bacon in oatmeal doesn't make it healthier. It's only healthier if you ate less bacon than you would have because the oatmeal made you feel fuller. Nothing can really neutralize the fat and salt content of a food...fiber just fills you up. It doesn't cancel anything out.
I understand the convenience factor of the hot dogs (which can be cooked in the microwave and are neat and tidy) the fact that you give it to your cats (not sure that's a vet recommended practice, either) and that it's probably something you eat yourself. Not to mention the fish probably love it...anybody know if fat and salt make food more appealing to fish too? I wouldn't doubt it, especially the fat.
Convenience aside, there are just sooo many cheap cuts of meat, or seafood that you could use instead. At least consider balancing it out with something like whiting, as Rachel said. Tilapia fillets are also cheap and low in Thiaminase.
Fat, salt, sugar, flavor additives (oh believe me, they are in there...a hot dog made of only mixed meat and paprika would taste like crap, at least nothing like what you expect a hot dog to taste like) just have no place in fish food. At least not ornamental fish.
Of course, if you are planning on switching over to Tilapia for your own consumption, fattening them up with what you find tasty makes total sense.