This is complicated.
1. rapgenius is probably the least spammy lyrics site on the internet, and definitely so amongst those on the first page of search results. As a consumer, I would not have a problem with Google, et al giving rapgenius results a special algorithmic bump to move them up. I also know that this is an opinion - it may be a popular opinion, but it is still inherently subjective.
2. If I was in rapgenius' shoes, I imagine gaming SEO would be a strategy to be seriously considered - one doesn't get into the music lyrics market without being aware of the current state of affairs. Barry Bonds believed he was the best hitter of his era, and if McGwire and Sosa were going to get credit for breaking the home run record while taking steroids, then damnit he was going to take steroids and hit 70 bombs. IMO, this is not a morality play.
3. But I do not care for the public personae of the rapgenius founders. They come off as juvenile and occasionally offensive, and I think they are bad representatives for consumer internet start-ups. I'm pretty sure this is a common opinion on HN, but I am not sure how much it should color our judgment of their actions.
As they say, the game is the game.