Dragonkind represents all types of dragon. The dragonborn was born with dragonblood in him.

~Tatsu

Dov could possibly refer to every living creature with a fair amount of Dragonblood in them, like Tiber Septim? Dovah would refer to Dragons, and Dragons only. No matter how Dovah related, it must be Dragon. Well, that's what I think at least. We might never know!

I think, I'm not sure, but I think that dov is talking about dragonkind as a race and Dovah is just Dragons. Like one might say humans, referring to one or to, or humankind, referring to the whole race.