Enemy guild players have a large red arrow over their heads whereas outlaws just have their name in red. IMO that's good enough, definitely agree on showing the opposing guild kill count in the UI though.

It shows he has 4 characters on the server so he should be allowed in queue, right? I'm about to get off work and try myself, hoping this isn't a new bug, would be game breaking for everybody who didn't get in before the queue started.