I had a similar problem with the usbloader gx not being able to recognize my games after a few months of it working.
Some things that helped me.
run usbloader-gx from the sd card
reinstall all the cios versions like the guides online suggest (using d2x-cios)
re-downloading it and reinstalling usbloader-gx into the apps folder
I don't know which of those ...
Short answer no.
Longer answer probably
At one point I had a third party, rechargeable battery pack that had a usb port on the back, it likely worked while plugged in but I have misplaced it and cannot try it.
You can probably cut a usb cable and wire it into the back of the controller. Drill a small hole in the battery cover for the wire. A resistor ...
If you hack the wii and use nintendont to load your gamecube games, you can play the games with a wiimote and nunchuck or the wii classic controller plugged into the wiimote as well as other usb hid compatible controllers.
Without using home brew you can only play with a gamecube controller.