My knowledge is very limited but essentially gaming or any music is subject to copy right. It pays to read the terms of agreement cause they tend to list information about using their material. If you do a lot of your own stuff that doesn't require any of these aspects then you virtually have nothing to worry about. But if so and you are in doubt you should email or contact them company that owns the rights to ask them if you may monetize off their material. If you make your own music then your safe, other then that you can search for royalty free music. Much more then that I have little information.
in the section you enable monetization at the top there is a section that tells you your standing with copyrights, keep up with that. They generally give you time to take down material that is subject to copyright to avoid strikes. Strikes will end up causing youtube to disown your partnership, so just keep up with it.