It is up to the sub to keep the dom in the loop, and IMO if I am befriending anothers sub, as a Dom...I should have the courage, honor, fortitude whatever you wish to call it, to introduce myself. As I said before I've never had negative feedback, furthermore I always ask the sub if they have a Dom if so who is it, and that I like to introduce myelf to them.
I'm always open, if they have a reason not to be or were tell me not to contact their Dom I would respect that, however I probably would limit future contact with that sub.