Ubisoft demonstrated how a player using a Wii U GamePad and another using a traditional controller can cooperate.
http://www.nintendoworldreport.com/news/30446
Ubisoft has officially revealed Rayman Legends for the Wii U. They also took the opportunity at their E3 press conference to show off the game using early Wii U Dev Kits.
Ubisoft specifically showed the potential for asymmetrical cooperative play between a player using the Wii U GamePad and another using the Wii U Pro Controller. Apparently, a player using the Wii U GamePad controls the game through the touch screen and has a special character who flies around the TV screen. This special character can interact in the game world in a way that reflects how the Wii U GamePad player swipes and taps on their personal controller screen. In this way, the GamePad player can interact with the game by swiping/slicing through ropes and vines, or by pull back on a slingshot that the other, traditionally-controlled character is sitting in. There are even certain platforms in the game that can be controlled by tilting the Wii U GamePad controller.
Ubisoft also showed off a special level of the game where the traditional characters had to run through a rapidly scrolling level. But this level was played like a rhythm game by the Wii U GamePad player, who tapped on the environment through the screen on the Wii U GamePad controller (in a method eminiscent of Nintendo's Elite Beat Agents) to clear obstacles and create paths that helped the other characters progress at a fast enough pace through the level.
Ubisoft showed off the game with just two players, but said the final game would support up to 5 players, presumably with one player using the Wii U GamePad and four players using traditional controllers.