You can do this with events and server mods. You'll need to have the setAppearance event (Can't remember if default or addon) and the Lock Appearance server config (addon). Set up the team spawns like normal, but also set an event on them so that when a player spawns, it sets their appearance to whatever you want the team uniform to be. Then, turn on the server preference for locked appearances so that players can't change it while in your server.