If this was me, my decision to out the agency would be based on their reaction... In this case, they seem to be doing nothing, which to me, makes them complicit. On the other hand, if the owner had contacted him and made some effort to reassure him that the girl was being dealt with, that might help. It isn't the agencies fault that one of their "independent contractors" stole from him... But it is their fault if they do nothing and it happens again.
Many years ago, I was down in London. Post session, I went to the bathroom. When I came back out seconds later, the girl was rummaging through my overnight bag (which is where i had my wallet). We both pretended that I saw nothing. After she left, I called the agency just to let them know. The owner told me that they had had one similar report a few days earlier... nothing stolen, but very suspicious behavior. They let her go based on my call. I continued to use that agency as a result.
Back to the OP... One thought about going to the Police... He may have trouble claiming this loss on his insurance. On the other hand, if he does go the cops, his insurance might argue that HE was breaking the law (C-36) so can avoid paying that way as well. Insurers aren't in the habit of setting claims for "criminal's" losses. Talk about a rock and a hard place.