NFC typically has a range of about 4cm (1.5 inches), so you should be fine. I can't speak specifically to the range of the Wii U's NFC chip, but I have yet to see a device that wouldn't read an NFC card due to a thin protective case over the reader.
As an example- when I ride the light rail, I use an NFC card to pay for my ride. The reader can read my card through my wallet (and a few other cards). I've seen some people successfully pay with their card through their purse as well.