Why would human terminal values necessarily have to encompass or be compatible with genetic terminal values?

Because sometimes giving oneself existential angst is more important than having reflectively coherent definitions for concepts.

If it's using heuristic proxies instead, and of course it is, since it's not possible to directly observe reproductive fitness, the proxies would then be human terminal values.

Well that's the first-level notion rather than the considered-on-reflection-and-full-information version we're actually aiming at, but yes. But just go along for the ride and pretend to be scared when Azathoth jumps out at you.

Don't you know darkness and terror are just more philosophical than mere knowledge?