Sabaton's historical knowledge alone could put them all up here imo

But it also depends on what kind of intelligence we're looking for. If we're looking for book smarts, then that would be the aforementioned Sabaton, and Brian May of Queen

If we're looking for Intelligence in experience, then that could be Bruce Dickinson of Iron Maiden considering how many side quests the guy does alongside being a vocalist

Or maybe musical intelligence? If that's the case, then someone like Jacob Collier absolutely qualifies. Same with pretty much every prog band, Rush and Dream Theater in particular. Hell maybe even Tuomas Holopainen of Nightwish could count for this as well.