I really don't know what to think. You can certainly play as one in Skyrim if you wish, but that isn't good enough in my opinion. Any hard evidence on this either way?

The Dragonborn has been described as 'the hero of man' in official sources. Then there is Wulftharth, Talos/Hjalti and maybe Pelinel and THEN there is the fact that the Thalmor were afraid that the Blades would find another Dragonborn (according to Delphine).

I think it's pretty obvious that, lore wise, the Dragonborn is the Shezzarine and, imo, should have Atmoran/Nordic heritage.

Hard evidence? Nope. Evidence? Maybe. Consensus? None.