This is an issue due to the new ART System. I did tests on a ROM that could switch between Dalvik and ART. When running android with Dalvik, Game Guardian worked fine. As soon as ART was running, Game Guardian would "crash". For me it just simply closes after saying ADB Shell has been root permissions rights. It then closes and no crash error. Until the Game Guardian Devs find a way to bypass the new security system that Android 5.0/ ART enforces I can't see this working for a while. If you really need to use GG then I suggest installing a ROM that does not use ART for the Runtime Environment.
If this is all wrong GG Developers then please let me know. This is just research I discovered when testing for the issue. I'm in college training to be a QA Tester for software. If you need me to test builds before releasing to public then feel free to let me know as I may be able to help with testing. I own a HTC One M8 Developer Edition w/stock Android 5.0.1 Sense 6 Update, HTC One M7, and Samsung Galaxy Note 3.
Regards
BinaryXeroMedia