IGN published a preview for "Tony Hawks Downhill Jam" today and at the end it has a bit of information regarding the titles online status.
IGN claim that third party developers will not be able to utilise the online interface for the Wii until well into 2007.
Of course I don't think this is going to affect first party support for online play. Super Smash Brothers Brawl is expected to be online with a Q1 2007 release. We will just have to wait for third party games.