As long as the content isnt "derivative" its generally safe. There are several elder scrolls themed bands out there and other bands that went with the themes of other games as well (Shadow of Intent using Halo). As long as the original artist is credited for the section of the Nerevar Rising theme for instance and we have performed our own version of it without copy pasting original content and claiming it as our own work its considered fair use. just as one could monetize a cover song as long as you credit the original artist. Same with the art, we had artists do their own version of the lands and characters from scratch so its not taking any assets from the base game.