Peter Whoah, how did you split the thread like that?
Now that I've taken a better look, I'm pretty sure there's some violations going on. Not that the affected people would care, though.
I mean, look at this:
If a picture of the Venus de Milo is a derivative work, then the game is definitely a derivative work of the graphics it's made of. In this case, the resulting game has to be both CC BY-SA and CC BY-NC-SA. But, much like binary blobs in the Linux kernel, there are different interpretations, and the copyright holders are not willing to sue for it.
It has been clarified that the GPL, by default, doesn't apply to the art, but CC BY-SA has no such limitation - it applies to the whole damn thing. That's why they added one-way compatibility with the GPL to BY-SA 4.0.
There are both graphics and music under a CC BY-NC-SA license. I'm sure the graphics are a problem, but maybe not the music. That's because the music only plays in the lobby, and one could argue that it's not really integrated into the game. But I'm not sure about that.