Splunkbase shows the add-on is compatible with 6.5, 6.4, 6.3. Just curious if it is also compatible with 6.6 but possibly Splunkbase hasn't been updated.
Yes, you are correct. The Splunk Add-on for Symantec DLP should be compatible with 6.6.X, because new Splunk releases are backward-compatible with add-ons that supports a previous version unless the add-on docs specifically say otherwise.
I've updated Splunkbase to reflect this.