The guy that got bit on the shoulder was the hispanic father. He hasn't been named, at least that I recall, but he and his wife and kids have been in quite a few scenes.
There was also the brunette and older black guy that I don't recall ever seeing before.
As to the zombies, it does seem like an awful lot of work for Merle to bring them down on the camp, but I gotta agree with the guys on the show and assume he's going to want revenge. Other than his brother, Merle doesn't seem to me to be the kind of guy that is particularly social or cares about his fellow man. He may assume that his brother could get himself out of any problem, or between the pain and any other drugs he's taking (remember when we first met him?) he may just not be sane enough to care.
I don't expect zombies to roam in packs, and I don't think that's an angle the show is going for. If one finds something, others come, but they aren't particularly organized otherwise. For them to wander that far outside the city in a group...seems out of place without some sort of help. Maybe they did see the fire...it was the first time they built it bigger. I doubt they smelled the fish (they've been cooking food all along, unless they ate the squirrels raw).
But yea, logistically it seems like it would be tough for him to do.
I particularly loved what they did with Guillermo in this episode. That's exactly the kind of writing that makes the books great - set up a situation that seems like it's going in one direction, take it in a completely unexpected one. It helps that the actors are all so damn good, making their characters quite believable.
Jim got bit - we just didn't see it. I'm betting that will be key next week. Also, will they show them putting Andrea down?