I figured it out! Drape all seem to drape all hair groups at once, while the drape tool only drapes your selected group.

Hmm, which brings me to a another question. Just exactly why can't I apply different hair shaders to different groups? I don't think you can apply anything major other than number of guides to different hairgroups, not even different length or thickness. Having different groups kind of loses the point, unless I'd want to create a really complex hairdo for some reason. Maybe like a wedding setup with extreme details.