I don't know.... That benefits Sega far more. Nintendo gets yet ANOTHER party game on Wii and one that includes Mario again while Sega not only will earn a lot of dolla-dolla-bill y'all for publishing the Olympics game, they also get to advertise their character, who has lost tons of credibility over the past few years, in arguably the biggest game coming out on Wii, which itself, so far, the most successful next-gen console. Of course, this opens up Brawl to more cross-over fans, especially those who have been yearning for a Mario vs. Sonic anything since the 16-bit era, but, like Snake, it just seems like Nintendo is giving more than what they're getting in return.
So if there was a deal, I would think that there's more to it than that. Although, this could just be Nintendo a case of Nintendo being charitable enough to help out 3rd parties.