It does not allow you to send a invite before entering the matchmaking or during the game. It does allow a invite after the game in the after action lobby. But in my experience yesterday (after about dozen tries to multiple friends, the invite were sent (and accepted) but not a single invite brought a person into the game.
I covered it a bit more in depth in this thread; http://answers.ea.com/t5/Plants-Vs-Zombies-Garden-Warfare/No-party-system-to-play-with-friends/m-p/2409423#U2409423
