From what I understand, someone in the Hanso family is responsible for the Black Rock. Also, someone from the Hanso family is sponsoring the Dharma initiative. I believe the Hanso family knew about the Island long time ago and kept passing the secret from generation to generation. The black rock was for no trading purposes and we can guess that from what Jacob's enemy said to Jacob. The black rock people come to the island with Richard Alpert on the ship. Jacob's enemy goes from the conversation in the beginning of the Incident part 1 to the temple or the donkey wheel. He tries to move the Island to evade the Black rock but realizes that it is inside the radius and ends up putting it in the middle of the Island. MAYBE he gets transferred to the outer world somehow, giving chance to Jacob to give the Black Rock crew free will. They choose to join him and become others although their reason was to go get rid of him. That's why they had dynamite. Richard Alpert might have been the captain and might have chosen to follow Jacob causing everyone else to follow him. Those who refused left as slaves in the ship to die there. He makes him special due to his loyalty and makes him be ageless but he can still get shot, stabbed and die. (Same with Jacob). Jacob and his nemesis were the only people on the Island at that time, maybe there were more natives there. Depending on whether you believe Jacob's nemesis to be transfered to the outside world or not, he came back somehow or maybe Jacob just killed him/ imprisoned him.
From their we can guess the connection between the others and the dharma initiative. The Black Rock crew with Richard's leadership had the same job as The dharma initiative but of course with less technology. That explains what Richard Alpert means before when he told someone that they came here for a reason not for some fertility issues that Ben was wasting their time on. Maybe a person who explains interest in the Island and not in what the Hanso family wanted to do (With the Black Rock or The Dharma initiative) has a chance to become a leader. Maybe that's why Richard cannot be a leader because he still cares about the work of the Dharma initiative and also why he was building a black rock model.
I hope you understand what I said and sorry for any repetitions I said. Thanks and PLEASE comment!