Sirithheruwen has it.
They are related by employment, if nothing else. And you are right. I was thinking of Nob's challenge to the two Black Riders who were bending over a prone Merry. It never really occured to me until I set this question that Nob played such a significant role, preventing as he did Merry's almost certain capture, if not death.
So, the thread is yours Sirithheruwen.