The plugin is not active on system apps.
To use, set channel (controller number) in the Aroma config menu (L + DPAD Down + Select) and toggle enable on.
If you're using this for multiplayer in New Super Mario Bros. U, New Super Luigi U, or New Super Mario Bros. U + New Super Luigi U, set the channel to the number of Wii U Pro Controllers/Wiimotes connected.
For example, if you have 2 real Wiimotes and 1 real Wii U Pro Controller, set the channel to 3.
GamePad to Pro supports two Wii U gamepads to be used in games as Pro Controllers as well, or even just the second GamePad to be used as an emulated Pro Controller.
This requires the Multi DRC setting to be enabled in the System Config Tool, and the second Wii U GamePad to be paired using the same tool. MULTI DRC MUST BE RE-ENABLED ANYTIME THE CONSOLE IS REBOOTED!
For legal reasons, the System Config Tool will not be linked in this respository.