By deduction, they should be the only humanoid race in Auriga... But...

There are other humanoids in Auriga: The Sisters of Mercy, the Ardent Mages, the Roving Clans. I could include the Broken Lords before their curse.

So... What does that mean? I can only think of two possibilities...

1) The humanoid natives and the Vaulters are different species but they evolved in a similar way and therefore look very similar.

2) The humanoid natives are from the same human race of the Vaulters but somehow came to Auriga before the Vaulters and, unlike the Vaulters, they completely forgot their extraterrestrial origins.

Thoughts?

The answer to your question is 2)

The race is called Mezari.

Check out this thread if you are interested in lore.

https://www.games2gether.com/endless-legend/forum/5-general/thread/2852-timeline-surrounding-endless-legend-an-attempt

Thanks, I will get a look!

Regarding the lore...

"Success" is the prison hulk that crashes in Auriga. Opbot is one of the playable characters in Dungeon of the Endless.

Later, in the Vaulter quest, in EL, he is reactivated. He later discovers the "Argosy" and comments that the Vaulters come from that ship... Why the sudden name change?

Sublustris wrote:
More then one ship crashed/landed on Auriga in the past, those are two different ships.

Ah, yes, makes sense.

Are humans related to Concrete Endless? In devblogs about Broken Lords and Roving Clans BL are referred to both mutated Concretes and part of the 'Rovers. Can it be..?

no, humans are not related to the endless for as far as we know.

the ardent mages, roving clans and the broken lords used to be the same people but this was a very long time ago, where they came from was unknown but they came from a different source than the vaulters.

Probably the same arch-race the Shadow were expelled from.