We need at least 1 WM that checks deck legality (and has access to all vaults), randomizes matchups and makes rulings. None of those can be done before war, vault access (other than your own) is a definitive nono for any participant. Event cards could be made before war (just gotta come up with 15 ecs and 5 super-ecs before you even start), I suppose market prizes is ok for a 'participating wm' to make so long as they have no idea in which team they end up (cant be masters), same for rule changes before the event.
Note that I havent talked to anyone about this, so 'participating wms' are not a thing yet, even though I'm the one accepting all the applications (and musing the thought). I of course want as many as possible to apply, but I think we need at least 2 wms without any conflict of interest.