I think the bigger problem that the OP pointed at is that whatever adjectives you attach to this, surveillance is almost always the wrong way to change behavior, unless your desired outcome is to make everyone suspicious of everyone else.

What's stopping these folks from creating an out-of-company channel to do the bullying and attacking in coordination via that means, or tricking the victim into joining them in the new side channel?

The answer to bullying or shitty office behavior is not monitoring. That cover-your-ass because the real answer is hard. Improve your company culture. Fire people who are detrimental to the team. KNOW YOUR TEAM! So often I hear about these things and what you find is a shitty manager who has no idea how to be a manager and says "well they get their work done."