Local (DCOM) connections are only supported for ArcGIS Server versions prior to 10.1.
About programming with ArcGIS for Server in .NET
This section in the software development kit (SDK) introduces some topics with which all .NET developers working with ArcGIS for Server should be familiar. It provides a foundation for ArcGIS for Server development.
See Also:
Connecting to a GIS serverProgramming with server objects
Managing application state
Working with server contexts
Licensing ArcGIS for Server
Best practices
Working with SOAP
ArcGIS for Server application performance tuning