It's a great idea from a marketing standpoint, that's what they're doing. They know that the competitive smash community reacted incredibly negatively to Brawl for the most part. By sponsoring EVO and appealing to the competitive smash community they maximize the good PR and exposure, effectively bringing them into the spotlight for every player who keeps up with competitive smash. By word of mouth alone they will drastically improve their public image in the eyes of their fans. You can see how this would increase hype generation and bring faith for Nintendo to the table, which will give people faith that maybe smash4 will be worth trying.
Not only this, but i feel that they have realized that endorsing competitive gaming while still embracing the fun aspect of the game at the same time is a better way to do business, as it appeals to a larger audience. Especially with the rise of sponsorships and interest from large E-sports teams like cloud9 and evil Genuises.
