EX Raid Question

No.

No, it's just like any other raid.

It sounds like you are describing a 'private lobby'.
This is the same feature available for every raid. Your group may suggest you use a private lobby.

We use them for most Mewtwo raids to prevent spoofers joining.

Apart from keeping spoofers out of the raid battle, a private group is set (with password aka code) to allow players of the same team to join forces with each other to maximize the number of balls obtained from contribution by team. E.g. at a Mewtwo raid, its quite common to find sizeable number of players from all 3 teams so it makes more sense to split the player base into groups representing their respective team color. That way, each player is assured at least 10 balls (6 from defeating the raid boss, 1 to 3 for damage, 3 for contribution by team; and if you belong to the team that is holding the gym, you will be allocated another 2 for gym control)

PS: for solo raids, it is possible to obtain a max of 14 balls if you belong to the team holding the gym