Response from support (Thanks, it works :-):

We do not bundle and ship the MS6 driver you are using with Mathematica (there are some licensing issues). Thus we do not support the same.

You should be able to use the jTDS driver which Mathematica incorporates to connect to your database:

JDBCDriver["Name" -> "Microsoft SQL Server(jTDS)", "Driver" -> "net.sourceforge.jtds.jdbc.Driver", "Protocol" -> "jdbc:jtds:sqlserver://", "Version" -> 3.1, "Description" -> "Microsoft SQL Server using jTDS - Version 1.3.1 - This supports \ Microsoft SQL Server 6.5, 7, 2000, 2005, 2008, and 2012.", "Location" -> "/Applications/Mathematica.app/Contents/SystemFiles/Links/\ DatabaseLink/DatabaseResources/sqlserverjtds.m"]

Website: https://sourceforge.net/projects/jtds/files/jtds/