BOY the ancient Hainish messed with so many human planets’ genetics.
Reparations WHEN?
The Ekumen isn’t even the Hainish reparations project.
The Hainish reparations project consists of showing up with a middle-schooler-made card that looks like this:
I realize that this was a joke, but to take it seriously for a moment... How much continuity is there between the present Hainish civilization and the society that did the expansion? The expansion was a really long time ago, right? Supposedly in the Ekumen's universe Hain is the real human homeworld and the expansion was when humans became established on Terra, which really doesn't fit with what we now know of genetics and human evolution, but maybe aliens took some Homo erectus to Hain like a million years ago and then the first Terran Homo sapiens were descendants of a back-migration... Anyway, that would mean the expansion was, like, 200,000 years ago. I think even working from 1960s knowledge of human evolution and ignoring everything discovered since it couldn't be less than tens of thousands of years ago.
I think, realistically, the civilization that did the expansion is probably just gone, in the same way the Roman Empire is gone. Sure, their biological descendants are still around (though after 200,000 years it'd be a toss-up whether an expansion era Hainish would be closer genetically to a modern Hainish or an Anarresti), but with that much time having passed since there's probably not much cultural or institutional continuity. The Hainish paying reparations to the Seggrians would be like the Iraqis paying reparations to Israel for the Babylonian Exile.
Also, are there really a lot of really biologically weird humans in that universe? Let's see, there's the Gethenians (gender-changing hermaphrodites), the Seggrians (very skewed sex ratio), the Hainish themselves (the fertility control thing, really reads as them having applied some mild transhumanism to themselves at some point)... I think that's about it? The other human populations in the setting look to me like more-or-less plausible results of 200,000 years of divergent genetic drift and/or evolution.