I don't install my GC games. I use the Nintendont WiiU Channel installed to the Nand, and boot all my GC games from the SD Card using the Nintendont WiiU Channel.
It's a lot easier for me to do it that way, so I don't have a bunch of GC Game icons on my WiiU Main Menu. And they all play perfectly fine. I have all the old Resident Evil games right now (RE1 Remake, RE2, RE3, RE0, RE Code Veronica X).
And on USB Helper has 2 different versions of Nintendont, it had the Channel Version, and the Forwarder. I chose the Channel Version, and it's been working perfectly for me.
EDIT: And yes, I play only on the Gamepad. When you choose the WiiU Channel Version and install it with WUP Installer, you can play GC games from the WiiU (Not vWii) with the Gamepad, it acts as a screen and controller, like most WiiU games.