Well I have just been adding some sub-categories (just a 2nd level down) on my ebay store. I have then gone to my OSC store --> ebay Get Categories and clicked on the "Update Categories" button but only the Parent/Top categories import, the sub-categories do not show (they are not in the OSC database) so I think we are both at the same stage!
I have not had any time to look in to this any further so far - just have to hope we'll be able to get it sorted.
Thanks,
Jamie