I think I'll believe when it's officially confirmed by namcobandai, but until then.
In an interview with Gamasutra, Takahashi(Katamari's creator) said: "I'm not really interested in [the Wii]. I don't think a controller should have that much influence on the enjoyment of games.
"I see what [Nintendo is] trying to do, but they're putting such emphasis on the controller: 'Woah, this controller lets you do this!', and I'm thinking - are you messing with us? So, there's nothing I really want to do with it right now."