The URL is looked up as requested, in whatever form — domain name or IP- it is requested. SGOS does not resolve URLs, via DNS, before sending requests to WebPulse.
Most content filtering databases keep very up to date and accurate IP address, so a forward or reverse DNS lookup is not required. You can test whether or not an IP address, or a URL for that matter, exists in the BlueCoat WebFilter (BCWF) database if you simply use the test-url command in the command line interface (CLI) or Management Console (MC). The test-url command returns the same category information as a proxied request would return.
"Note: The latest implementations of SGOS provide two optional configurations. The first is a Dynamic Categorization (DRTR) request, and the second is Malware Feedback. You can choose to independently enable or disable both of these message types via the checkboxes provided: