I don't think there's anything in our current (intentionally open-ended) constitution that should prevent any ninja from helping in diplomacy.
Whether that help is drafting letters, sending harassing PMs to General_W to get his butt in gear, or even chatting with other teams.
The only caveat, imo, is that anyone other than the elected Daimyo should make it clear when talking to other teams that they are NOT the official representative of team SANCTA. That'll make it easy for us to back-peddle if someone goes off the reservation and says something stupid to another team.