I don’t think Romeo is part of Locke’s team for a couple reasons.
I think that, for one, because already had a Halo game with the two together. No, this by no means rules out the possibility, but I think it would give the game a bit too much of a familiar feel. I’m getting vibes from the marketing campaign that 343 wants Halo 5 to be something totally new and surprising.
From Locke’s standpoint, he is the leader of the team, but Romeo would naturally regard Buck as his leader. Locke, being the ONI agent he is, would have definitely taken this psychological fact into consideration. He needs a team he can keep tightly revolved around him.
Finally. Macer or Tanaka? Why not both?