the main reason to load figure and hair, then make figure invisible, is to assure alignment of hair render and head render.  if hair is loaded without figure, it may be in the wrong place, wrong distance from camera, et al.  unfortunately, such a composite product of two renders is gonna look fake, like one of the banners I just saw on the upper right, where a wig of various colours was pasted over a face with different lighting than the wig.