Ok. Let’s break it down :)
A corn dog is a hot dog on a stick with a breaded coating. This is much different than your average bread. The coating is more cornmeal, eggs, and buttermilk, no yeast, no wheat, no fermentation. So I would say it is more unhealthy than a slice of bread.
Then you have the hot dog. I watched a recent episode of “How it’s made” which showed how they make hot dogs… and for a week I couldn’t even think about eating one. It’s all the bits and pieces left over from animals and trimming, and often some organs too. Not things like brain or eyes though, but it’s not the healthiest of meats.
One corndog (here in Canada we call them Pogos :) ) is anywhere from 200 to 400 calories (if it’s baked versus deep fried, if it’s portioned with robots versus made by a guy in a truck, etc). Imagine someone has a meal of two pogos, mustard, a Coke, and fries. This meal can easily hit 1200 calories (600+ for pogos, 0 for mustard, 140 for a can or 240 for a 20 oz cup of coke, 300–500 calories for the fries), more if you use ketchup or honey mustard. Even just the two pogos is not a great amount of calories for the food you get in return.
Look at it from the food group perspective. Does it contain veggies and fruit and dairy? Nope, it’s wheat/grains and meat. That’s not balanced, which is an indication of nutrition generally.
Then there is the nutrients themselves, which are sparing due to the high amounts of processing the item goes through. Still, they could put in some extra stuff, but I would bet only manufactured ones would, because Uncle Bob in the truck at the fair doesn’t need to provide nutrition info at all. There will be iron because of the meat, and often Riboflavin because of liver and kidneys. The cheaper you go, the more sodium there will be.
Overall, corndogs are not good for you. They do not provide you with a range of nutrients, the quality of the parts is generally low, their method of cooking can add unnecessary amounts of fat, and a corndog meal rarely consists of a balanced amount from all the food groups. Once in a while, sure they’re fine. Maybe even twice a week for lunch if you eat one pogo and no coke and a salad. But eating a fatty corndog meal with coke and fries every day is a sure fire way of having heart attacks.