I thought about this a lot recently after someone said it, ::: spoiler my opinion is that
No, a hotdog is not a sandwich because it is meat inside of a single piece of bread. If you accidentally broke the bun into two pieces you could argue that you've made a hotdog sandwich because the meat is still called a hotdog and you've got two pieces of bread. That some sub sandwiches are a single nearly split piece of bread I view as an implementation detail moreso than a defining characteristic and not enough to say that sandwiches can be a single piece of bread.
:::
Bread is a requirement for something to be a sandwich, so you'll have to convince me that a tortilla is bread. You might be able to make a case for the soft flour tortilla, but I just don't see how hard corn tortillas can possibly fit under the umbrella of "bread".
I've seen all of these used to make what can only be called sandwiches. Bread is certainly popular for it's dry and durable structure, but it's not a requirement.
Sub bread is often split. It's just the type of roll used. I'd consider Hot Dogs a small sub or hoagie, just like a sausage, peppers and onions hoagie.
Their seems to be no end to the sandwich debate but I want to point out that their are many sandwich, hot dog included where the bread is not separated. I would said a sandwich is made of two parts. That includes separated sandwich like club sandwich, and non-separated sandwich like baguette sandwich or hot-dog.