I have seen a certain level of what I would term insecurity, but my opinion is hardly definitive. If a dom and a sub agree- mutually- to be exclusive I can understand not playing with others and so forth, but banning people from using IMs, Whispers, PMs, and so on seems a little over the top.

Trust is fundamental in any relationship, and vital in a BDSM one. I personally prefer to trust to my partner's discretion, but everyone has their own methodology. As long as it's working for the two people involved; that's the only meaningful yardstick, in my (highly overinflated and self-important) opinion