No, you're misunderstanding me. Only 1 (as far as I know) modder has implemented the ability for a Wii game on a Wii U to read controllers in the GameCube Controller adapter. The games he got them to work on were Brawl and Project M (considering they're the same core game, it's more reasonable to look at it, as if they got the functionality working for one game specifically and more or less copied the work into the other title, that kind of copy and paste job would not work for other completely different games though). I'm sure if you connect the GameCube Mat to the adapter in your Wii U for that build of Brawl or Project M, it will read the inputs for those games, of course it'd be a completely impractical way to play those games and lacking many button inputs, but it should be usable in those specific builds.