ah, if you have a vWii forwarder, the gamepad will be disabled, but you'll have access to USB.
If it's a WiiU forwarder, I think I added gamepad support. maybe I'm not remembering correctly?
vWii forwarder is actually launching vWii -> UNEO forwarder -> Boot.dol on SD.
You are on vwii, and USB is available.
WiiUVC channel on the contrary is using a sandboxed vWii, using a patched IOS255 (can't be changed), and only has access to SD card or Internal (seen as Disc).
With WiiUVC, the gamepad video and controller should be possible.
Injecting USBGX in a WiiU WiiVC channel is useful to make a Nintendont GUI launcher for games on SD only.
It generates a different ninconfig.bin file for each launched game, instead of using the same config file for all "injected ISO" channels.
It can also generates cheat codes, etc
that's the main advantage of using a loader as GUI instead of individually injected games.
But I don't remember if gamepad is working, sorry.