Personally, I think one can learn enough about agile to apply it usefully without ever learning what a "scrum master" does. Maybe this goes back to the discussion of process vs. best practices.
Maybe. But it's a pretty critical role, and if no one on the team is filling it (or even aware that the role is needed), you're losing out on most of the benefit of agile. To the point where it's not really what people mean when they refer to the Agile process.
