MSSQL Mirroring equivalent to Oracle Data Guard Snapshot Standby Does MSSQL support an operating mode on the failover partner / mirror that is functionally equivalent to Oracle database's Snapshot Standby mode? 

ie A temporary active copy of the replicated database that can be open for read/write but can be reverted back to a replication target without rebuild?
Mirroring does NOT have this capability.  If you are using the Enterprise Edition of SQL Server then an Availability Group (MSSQL's successor to mirroring) with a readable secondary would do this, but you would be required to license both instances with EE licenses.