After modding 2 identical Wii's with the exact Modmii setup, I can get the gamecube controllers to work using usb-loader gx on one, but not the other. This is for SSBB game. Below is the system check of the problem Wii.
SysCheck v2.3.2 HacksDen Edition by JoostinOnline, Double_A, R2-D2199...