At the beginning they said they're available for any creative purpose, but now I don't see anything saying so, and the help page says: "YouTube cannot give you information about legal liability or other issues that can occur off the platform. You may wish to consult a qualified attorney if you have questions about your use of music."
Your best bet would be to ask them. As a side-note, I too have been wanting to know if it's available for games.
Source: link (beginning blog), link (current help page).
Moderators, you must have so much patience to be able to deal with everything. I mod in a server of sorts and today we just got a message, which, despite it's helpful constructive criticism, basically stated that all of the mods were jerks and that was the only reason our server was unlikeable. So, thank you, for having patience. You are appreciated!