Other players in the FFA could form their own teams.
Having a team beforehand would still give an unfair advantage.
Also using that logic, multi-accounting in an FFA should be fine aswell.
And in a 3FFA, like the game shown, this argument falls flat completly.
Provability and official rules aside, if you form a team before the FFA game starts, thats just unfair towards the other players.
That is what team games are for.