Using Oracle SQL Developer with MS SQL

1. Download a JDBC driver for MS-SQL.

2. Load jtds to SQL Developer. Perference->Database->Third Party JDBC Drivers.
Once you load the jtds-1.2 jar file you should see both SQL Server and it's aging uncle Sybase added to your list of options when creating a new database connection. 

3. Setup Database Connections
Select the SQLServer tab, Set "Port" as "1433;instance=instance_name"


Reference:
1. http://thinkoracle.blogspot.ca/2010/09/using-oracle-sql-developer-with-ms-sql.html