So contrary to what I would've thought from Nintendo, they actually do a straight-forward outline of the supported controllers here:
○Wii U GamePad (Max 1)
○Wii Remote or Wii Remote Plus* (Max 7)
○Wii U Pro Controller (Max 7)
○Nintendo GameCube controller** (Max 8)
○Nintendo 3DS series system*** (Max 8)
* Includes expansion controllers (such as the Nunchuk or Classic Controller Pro).
This is good news, as it means I can buy more Pro Controllers instead of investing in Gamecube controllers just for this game, but I'm still confused on whether the Wiimote requires a Nunchuk or not.
I wonder how they display the player numbers on the devices.
EDIT: The "Controllers" page there actually outlines that you can use just a Wiimote, which seems crazy but awesome.