Are they the same beings?

I ask because I need to know if it would be against Lore to make a creature-character model of the Yokudan Goddess of the Air, Tava.

I already know a bit about the Yokudan Myth Lore. But I haven't found legitimate conformation that the Yokudan Deities are the same as the Nine-Divines. The only reference to it is how they are "sometimes" associated with the Nine-Divines, such as Arkay or Kynareth.

I don't think so. Some of them are mirrors of their selves in the Cyrodiilic pantheon, though. Think about them as different aspects of what might be some great oversoul-god-thing. I think Tall Papa <--> Akatosh <--> Alkosh <--> etc. is an example, but it's been a while since I read up on Yokudan lore.

So, for their to be a mod where you physically encounter the Yokudan pantheon wouldn't break Lore?

They have many, many deities. You can draw parallels between a couple of figures, but it's not like the clean parallels between the Aedra/Eight Divines in the Altmeri/Cyrodiilic pantheons.