In terms of indie bands using this to promote their song, I can't say for sure, but I did find this resource that certainly contains some bands I'm not familiar with. Perhaps some of them are indeed by bands with myspace pages trying to push their craft in new ways.
A major difference with this game and the idea I explored yesterday is the quality-vs-quantity trade-off. Songs are distributed with the actual audio data included (so 5+ mB downloads and questionable legality) rather then just the gameplay 'track'. The experience seems to more closely mirror that of GH then what I proposed, but I came across at least one person on the forums bemoaning the fact that there weren't more songs available.
Update: Is this a sign of things to come? -- In line with the points brought up in the comment thread of my previous post, I'm willing to bet this is not the last time we will see Guitar Hero (or similar gameplay) used as a promotional vehicle for important pop-culture music brands.