There is a really good podcast called DeCrypted by Ars Technica's TV podcast that deconstructs and comments about each episode.
One of the theories out there is that the Man in Black is a first generation A.I. host from the period of time that Anthony Hopkins's character talked about when he and his partner were still developing the hosts and world. He talked about his partner's attempts and theories about wanting the hosts to eventually become fully self aware. The thought is that as first gen hosts, their "skin" was stronger than the new hosts. As we saw in the last episode, the hosts can shoot the guests, but it's more like a paint ball or bean bag on humans. The theory is the hosts have softer skin and internal workings than humans and that's why they are actually "killed" by the same bullets. It's also the reason why so few "hosts" have access to bladed weapons...knifes, axes, etc...that could actually do harm to the guests.