Are DNS and other services needed? I inherited a Mac OS X 10.8 server that is now only used as a file server.
Within the Server Apps settings it has File Sharing, Contacts, DNS, Mail, and Software Update services on.  We have enterprise DNS servers which I configured in the general network adapter settings.  

Why would I continue to have DNS service "on" if I can rely on enterprise DNS servers to supply DNS routing for this server?  Also, do I need to keep running the Mail service for any reason (e.g. maybe so it can send server notifications, etc)?  And would this be the only reason to run the Contacts service?
None of the services (except File Sharing of course) is required. The only thing you have to add are proper DNS server settings in System Preferences > Network > interface > DNS and the Mac OS X server's host name in your enterprise's DNS database.

For server notifications you can use any valid email account (e.g. your admin or a special notification/monitoring account) in your enterprise.