The fact that Arcocephale practices slavery is interesting. Does this put them in the evil category then? Well maybe, but then again, by the standards of real world history around 3000 BC, maybe they weren't that bad. But it's a tricky question.
For the purposes of two faction game (which I admit may be over-simplified for a philosophical discussion), probably not since they would probably still oppose EA Mictlan's blood sacrificing demon holocaust. But then again, maybe Arcos would be indifferent or neutral as long as Mictlan's rituals didn't impact their way of life.
Of course when we're thinking about Acroscephale, we're also thinking about the ancient Greek city states that it was modeled on, so then things get more complicated if we want to get specific about which city-state and if we can really draw any comparisons. In any case, this is pretty interesting stuff.