I'm going to go with no. For a full account of the Weapons Policy at MegaCon, go here:
They state in bold not to bring real swords, sheathed or not, a real weapon is still a real weapon. I'm kinda bummed myself, I would have loved to bring the actual Master Sword with my Link costume, but I'm going to have to bring a prop sword instead. Best thing to do is make/buy a wooden sword. Though even then, you have to transport it to/from the con in a bag for security's sake.