Symantec DLP for web (prevents data loss through http, https, ftp etc) can also be integrated with Websense solutions(Websense URL Filtering). In case an organization is running Websense and not in a position to remove it, then using Symantec DLP, websense can be integrated and data loss can be prevented through web as well.
Websense integration is supported officially from Symantec DLP version 11.5
Prior version also supports integration with Websense, but was not officially supported by Symantec.
I would like to share a document here, where Websense integration with any third party data loss prevention is explained. Third party DLP solution also includes Symantec DLP. These changes in settings are required to be made on Websense.
I also understand that changes in Symantec DLP side is known to all.