I think Doom3world had several tutorials.
I'm pretty sure I seen there the tutorial about bones of the head wich must have the same name as some of the bones of the body.
However, it is possible to figure out the analysis of .md5mesh.
I've done heads for monsters but always integrated, never separate models.
Separate animation channel, talking heads, tracking the eye at the object, focusing, cinematics - separate heads provide these features, as I see from the original game.