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.