Why should they be able to do that? It should be possible to add support without violating any Nintendo copyrights or trademarks...
I don't say that would be illegal, but if there is a videogame console with "official Wiimote support", Nintendo could (and probably would) sue that company. They don't have to win, they only have to make the small company spend too much money in lawsuits so they settle or go bankrupt.
I would love Wiimote support in the firmware, but I don't know if that would be a wise movement.
Maybe if they advertised it as having "official Wiimote support," but simply including Wiimote drivers (as well as other gamepad drivers) and claiming that the Pandora supports many types of input devices, including the Wii controller, Xbox 360 controller, and others, should not be a problem.