The zombies that we fight are members of the Talons. Radia's sky pirate crew (they wear the green uniforms).
So they aren't any indication of who the Mhachi were. The statues though. Seeing all those Hyur highlander statues in Weeping City convinced me that Hyur highlanders were the dominant majority in Mhach.
To be honest I like the idea of a nation inhabited by Hyur Highlanders using black magic. The statues certainly conjure op intimidating and imposing images of tall muscular black robed Mhachi black mages as highlanders.

About Calofesteri: It doesn't make sense for her to have been a lalafell. If anything her body and face have way more in common with female Hyur highlanders. Of course it's possible that ancient Mhach had lalafell inhabitants, but I want to believe that it was predominantly a hyur highlander nation. Nym makes more sense as a Lalafell nation if you look at the mutated tonberries. Powerfull black magic doesn't have to be associated with lalafells.