As Domme, I have noticed I have had different rules for each sub. One I might restrict a bit more as far as "playing" with other Dom/mes, but as far as talking, they are allowed to talk in open chat but no private chats.
I would like to mention that I seem to be more strict with this type of rule with my female subs rather than my boy.
I dont know why this is except that I seem to trust that my boy could handle himself a little better against a persistant Dom/me than my girl who seems to get uneasy when approached, so for her comfort we have made the rule of not talking to Dom/mes other than on a superficial level with the exception of my friends that I know and can assure her that are safe.
Now my boy can speak with anyone he chooses, however he is not allowed to be disciplined in ANY way by another Dom/me, he can talk adn tease in open chat as he pleases, but if there is an issue and another Dom/me tries to exert a discipline, I am to be told and I will take care of it accordingly.
So i understand the idea of not letting a sub/slave not play with another Dominant, but not speaking esp in a public chat or telling a sub that they cannot talk to someone that they have developed a friendship only with before the Dominant came into their life is a def sign of insecurity or mistrust of the loyalty of the sub/slave...
just my 2 cents!