Of course not. I think your mind is on a different playing field.
We're talking about Guild Sparring, pitting guilds against each other. Not teams. Essentially you'd be stripping away the difference if you can just band together solely for the tournament.
Also, I didn't see a mention saying that you can't join whatever they want whenever they want...just a statement saying there will be a time lapse you must be a member to participate in the GST.