The original link isn't a listener, it's just a camming aid with the same functionality most viewer-radars already give with a double-click on the avatar's name.
Some viewers have camming limitations(based on draw distance). With Singularity set to 300m, I can see the full sim, i.e. from a market 3km up, I can cam the ground, rez the build and all avatars.
As for chat-listeners, I'd be wary of any sim owner/admin using them under the pretence of moderation. When a mod is called, the RP should be notecarded. And this is assuming a mod is called at all, as most 'Goreans' have cut out the middleman and self-moderate their own RP.
It's rare, but I have seen sim-scanning devices rezzed on RP sims, from Thomas Conover
. They appear to give the monitoring functionality a sim owner might want, but could as easily be used for nefarious purposes. Sim owners should keep auto-return on, or risk becoming a host for these types of devices.