Yes Diebuster is in the game and you are right the copyright i wrote is credit for that. But there is no copyright that says Khara. I found 2 more copyrights in the game that say GAINAX and something else but it's in Japanese. It is too long so it doesn't seem it says Khara and i think it should be in english too if this was the case.
If anyone is interested they can check the copyrights in the trailer that appear at 11:19.