That's correct; it does work that way if you have an obj with all of the correct groups.  It doesn't, however, work to have an obj with only the head and neck and an actor with all the parts listed.  It says the vertex count is incorrect then.  I don't know if just using "Clear" on all of the parts that aren't necessary works.  I'm going to try that as soon as I'm to a good point with testing something else, and I actually get some sleep.