Do I need wii sdk or modified Unity to create wii games?

What tool so I need to build wii games that can run on the wii hardware?

Taken directly from the Unity website:

"If you are already an authorized Nintendo developer then please contact us today in order to evaluate Unity content authoring for the Wii console. Authorized developers, or anyone else with questions, can contact us at sales@unity3d.com for additional information."

You need to be an authorized developer with Nintendo before you can even consider developing on the console: with or without Unity. More details about becoming a Nintendo developer can be found here.