I very clearly remember that the JDBC driver that is provided by Microsoft for SQL Server has some dll's to be installed on the server (DB Server). These dll's are installed as external procedure on SQL Server DB.
it is present in the zip file of the JDBC driver and has a readme also, which clearly defines (in a cookbook style) as to what command requires execution on the server end for these procedures to be installed. These procedures are installed in master schema of SQL Server so that they are available to the client connecting to any other schema of SQL Server.
It has nothing to do specifically with the portal server, if you would take some other better JDBC driver for SQL Server (Type 4) then you would not need to install any component on the server.
Hope this helps,
Kapil.