At no point was the guy who grabs ahold of Dolores shown to actually work for the park. He could be a host for all we know. Remember, right after William shows up and that guy leaves, Dolores sees the little girl drawing the maze symbol on the ground, then when she looks back up, the girl has vanished completely. She's been to that town before, which means she's been off of her loop before. Like I said, it doesn't necessarily mean that William is the Man in Black, but it's clearly obvious that she is remembering shit that she has seen before, so this can't be her first time off of her loop. The fact that the park has been open for 30 years, and she's one of the very first hosts, means that she could have awakened a dozen times a year, every year for as long as the park's been open.
Also, the head of programming for HBO has already commented that he's impressed with how close a lot of the fan's theories are to what actually happens, so it's obvious that the people with their "wild theories" are closer to what's actually occurring than people who are the "Me think only like caveman" group.
“There are a lot of theories out there, and with some of them, I’ve been very impressed with how they’ve constructed the guesses. I’ll just say, they’re getting close…. I think people will get the answers they’re looking for by the end of season 1. A lot of the ones that people are buzzing about, I think you will get — I don’t know if ‘answers’ is the right word, but maybe it’s ‘satisfaction.’ You’ll see how Ford and the Man in Black play out by the end, story-wise.”
