I’ve been wondering the same thing. Scummvm does have a working virtual keyboard but I haven’t looked yet into getting it connect to a usb controller, or if custom mapping is even possible.

Details here : http://wiki.scummvm.org/index.php/Virtual_Keyboard

I’m prepping to set up scummvm this weekend and am hoping to sort this out. How did you end up setting up your usb controller to work in scumm? I haven’t been able to find much documentation on custom controller mapping.