As a reader of both universes... Halo would get rekt. I'm UNSC and Covenant times, it isn't even a contest. They'd get steamrolled by the Old Republic/Sith Empire. Forunners? They'd get beat by the Galactic Empire at its height, or the Galactic Alliance, or the Yuuzhan Vong. Precursors? Doubtful they'd win. Only - and I mean the only - possible argument made for Halo is the Flood. The Flood I think can take on virtually any group except Star Wars. It's doubtful they'd ever get past the Star Destroyers. And an Infected Jedi would have at best remedial force powers. The flood with guns have poor use for them, it would be even more pathetic with the force. It would be random twitch impulses with the force, and would accomplish nothing. And worse comes to worse, Flood can't infect Droids. They'd get rekt by the Trade Federation, who barely qualified as a power in Star Wars.