I can't say for sure how their facial morphs were made, but their textures and normal maps are certainly unique to them.
In player_creation.xtbl, there are morph keys for their morph presets ("morph keys" being the morphs at either end of a slider. eg: Skinny to Fat). (I meant to see if I could get those to work for the Playa, but forgot all about it.) So I would imagine they were made with the same system as everyone else. But who knows?
Edit: I've since tested the Story Character Morph Keys, but couldn't get them to work.