The GameCube's disk doesn't spin backwards. But it does "read" backwards. "Track 1" (if we want to call it that) would start on the innermost ring with a regular CD/DVD, but with the GameCube, it's on the outermost ring.
There are some bootleg GameCube "disk images" floating around on the internet, in some of those places where you can download illegal stuff. They're not really "disk images" though. They won't work in a GameCube. Nothing (except a GameCube) can read a GameCube disk, so some hackers used the very-hacked Phantasy Star Online to get inside the GameCube, then managed to order the temporarily-hacked GameCube to transmit the entire contents of various GameCube disks over the modem into the computer the hackers had just used to hack Phantasy Star Online.
Supposedly, if you take one of these bootleg "disk images" and run it through some of the homemade programs these hackers have been putting together, you can sometimes extract various bitmaps and audio files from the game. So, it's apparently "possible".
That's about all I know, and I wouldn't suggest digging further any further into it, as it's rather illegal, and even if you ignored that, you'd have to deal with some really hardcore bad guys.