I have to admit that I started out trying to do Conan d20 and am now increasingly doing REH:s Conan in Microlite. Anyway, I don't think the distinction is very important, I have always moded Conan d20 to fit my game and my vision of Conan anyway.
On further deliberation I think you're right on both points (I dont necessarily belive that "race" or ethnic origin is all that important in the "culture", they ar actually rather literary stereotypes).
Zamorians should remain +2 DEX, Picts should be +1 DEX, +1 Survival, +1 Subterfuge.
Barbarians should be +1 STR (sob...
), +1 Physical, +1 Survival.
This even catches the Cimmerian love of climbing, since that is done with physical
Barbarians would certainly include Black Kingdom tribesmen: again the distinction is more in genre cliches than in actual ethnical difference. "Picts" would be a catch all for skulking jungle-savages.
I'm sure that some groups/types have fallen between two chairs here: Himelian Hillmen for one...