Maintaining consistency of a story between multiple GMs is incredibly difficult, especially when the story has a span as long as the Zuma's.
How is it difficult? IMO you provide the background story... one person provides the goals, restrictions, and intent... and then you allow freedom of the GM's to interact and develop character atmosphere as needed.
The main GM has the control... the other would provide the chances for screwed up relations and mistakes. *shrug* makes sense to me... helps create the story while not micromanaging the entire thing... and leaves all the openings needed for people to change the world.
Poll