It is possible to use one drive if you install all your Wii and GC games as vWii injects. Will be along process though as you will have to create the inject for every game. Unsure if it you could store your roms on a Wii U formatted drive and transfer them over via FTP as I haven't tried. You could however setup Wii emulators and use SMB to connect to a shared folder on your pc so you wouldn't have to transfer them at all and just load them over network.