Let me clear things up here.
Usually, shooters have what is called a "spectator" mode. This means players can enter the lobby and spectate the game without being a player. For tournaments, there are people who "commentate," or call the match. They are called "casters." Usually, the tournament will have someone be the "spectator" and watch the game using spectator mode, while the casters watch this view and call the match.
Splatoon doesn't have a spectator mode. For a similar system to be implemented, a player would have to occupy one of the slots in the game without participarting so that the game can be "spectated."
Of course, this obviously won't work very well. For a 4v4 match, there won't even be room for an additional spectator (usually when there's a spectator mode, viewers are not counted in the lobby population).
What will have to happen is that the broadcast will have to take the feed from one individual setup, which means they'll have to watch the tournament from solely that player's perspective, unless they get a ATEM/Tricaster or a bunch of HDMI splitters or something.