Doesn't namespace service=namespace server?

I'm confused by something.  This is Server 2008 R2.  I was of the understanding that a DC that ran the DFS Namespace service was considered a Namespace Server. 

I just went into DFS Mgt and noted the namespace servers for our 2 namespaces.  I was then looking at a DC that was not in that list, and it is running the DFS Namespace service (the services is started).

Isn't a DC that runs the DFS Namespace service considered a Namespace server, in a domain-based namespace?
If it is running that service, what is a possible reason(s) that it is not in the list of namespace servers in DFS management?