I've never used anything like this, but, it sounds like you'll want and "active" KVM switch as opposed to a switchable Hub since you'll want to share a screen. XIM3 has a standard hub IC on it, but, I have no idea how those switches surface the devices connected to them. Like, can you connect something like a G13 to the switch and it'll show up as a G13 on the output? Or, is it strictly expecting mouse and keyboard USB HIDs on those ports? If so, does it simlpy passthough (you get the USB descriptors of the actual hardware), or, does it convert (you get back "fake" USB descriptors and you lose the original identity (and possibly features) of the original hardware)?
So, to answer your question -- I don't know. :)