We are far from categorizing everything, mostly due to the constant changing of URLs purposes, what they post, new domains popping up every day, etc.
You will still need to make sure the other clients' IPs are in the internal network subnet(s) you told us about, the policy covers them and that their web traffic flows through the router we are tapped into. As long as all three of these are satisfied, the Web Gateway will monitor their traffic and record it.