I got one!

There is an offshoot of the Viera know as the Feol. Going into too much detail on their background would be spoilers to Revenant Wings, so I'll keep it minimal; they were violently ostracized as a people, and thus, they built their warren within a volcanic region to deter anyone from harming them again.

The map of Othard shows an area called "The Burn." It's a grey area west of Yanxia and southwest of the Azim Steppe. The corner the Dotharl have settled is the right spot to act as the border of the regions, so "The Burn" appears to be that desert as a whole.

The Feol-expy I imagine that they were one of the races of Yanxia, but fled to The Burn as the Garleans rolled through, or that they fled the Azim Steppe as the Xeala's violent culture forced them out.

Or both. The tribes of Yanxia ran to the Burn to find safety with their Viera siblings that had left Azim in a time before.

That's how I'd add them at least.