Er, I don't get why there's a huge fuss made over this. The source code is offered up free without any requirement to mention the original creator.
http://www.cheatengine.org/faq.php
Also, his stuff isn't required to be open source because he's not working on his trainers as part of the cheat engine project. That stipulation is only for people who want to contribute to the project.
http://forum.cheatengine.org/viewtopic.php?t=58063
He's not doing anything wrong.