In an attempt to protect artists I tried to make a point about when the license applies in the Guidelines(needs some more work apparently) . I don't think it's necessary to put all work that is created here under the license in question. Basically the license only needs to apply to everything, that ends up in the game(=is distributed with it).
According to the license, every kind of usage(including commercial) is allowed, under the following conditions:
Attribution — You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work).
Share Alike — If you alter, transform, or build upon this work, you may distribute the resulting work only under the same, similar or a compatible license.
I've always been unsure about how to handle the attribution part. I could provide real names for most, if not all work that has been done...