I don't know any reason for LinuxMCE to not support USB hubs, because it is based on Kubuntu.
It will help to find out if Kubuntu has this problem too. It is possible to report the problem to them and we can get a fix in one of their updates.
Let us know if you have this problem before installing LinuxMCE RC1.
I had this problem with pluto. Solution was to move the usb hub to a windows box to serve the media files.
Thanks for your answer, Joseph. if I understand clearly by some reason LinuxMCE doesn't support USB hubs? I was planning to use PC with LinuxMCE for others tasks as well.