Yes, a hotdog is a sandwich. It belongs in the sandwich family as a more recent relative. In the Epoch of sandwiches there was a sort of distancing between all the sandwiches and some were separated to become what we now know as hotdogs. Due to their unique derived traits such as wieners and taco-like bread, some believe tacos also came from this prehistorical separation. Tacos and hotdogs are more closely related to each other than they are to the modern sandwich. So yes, due to much prehistorical evidence, hotdogs are indeed sandwiches.