From the rules section on the jam page:
3) You game has to primarily use the default RTP assets of whatever version of RPG Maker you use to create your game.
The character generator parts are part of the RTP assets, so yes, no issue there.
4) You CAN use custom assets, but they should be mostly supplemental to the overall game or limited to certain scenes. This is mostly meant for tilesets and character sprites, custom music and sound effects can be used without any limitations.
So yes, you can have custom music. Good luck with your game for the jam!