The Pokemon website has updated and provided us with more information on some of the Wii/DS connectivity of the title. Now, the page mentions a need for software on the DS, yet does not tell if this software will be included with the Wii game, downloadable from the Wii, one of the DS games, or need to be separately purchased. Personally, we're assuming it'll be downloadable, but the article does make mention of it acting much in the way Wi-Fi does in Pokemon Diamond & Pearl.
The site also mentions that you can bring some of your Pokemon from Pokemon Diamond & Pearl into the Wii game through the use of 'coliseum mode.' This allows you to bring 6 of those Pokemon into the game and persistently record their battle information through Pokemon Battle Revolution.