Well this is strange. There are four players in a force called players and four players in a force called observers, But, Whenever I host his game in UMS the observer force doesn't appear even though all the players have start locations and triggers. And the allied and share vision check boxes are checked for the observer force.
So why won't the observer force appear in the lobby?

Maybe wrong player settings?
Make sure they are all set to human.

This sounds dumb, but is it .scx and not .scm?

Thanks Nude, I found out that they were on Unused instead of human.