So I found the problem.
I load my games on a fat HDD, files are .wbfs. When I used Guitar Hero 5 on a wbfs partition and loaded the game as an iso, it worked. I'm guessing it doesn't like .wbfs files?
edit: decided the best workaround was to create a second partition as wbfs. usb loader gx loads multiple partitions, so everything looks and looks great! If anyone is having the Guitar Hero 5 loading screen issue and all other solutions failed, this worked for me.