No child is allowed in my house or on my property if they are unwilling to follow my rules. I know this sounds very authoritarian, but honestly I've never had a problem with kids finding me too strict (then again, my kids are still too young to be free-roaming, so most of the kids who have been in my house are children of my friends). When another child is in my house, regardless of whether or not he was invited over, I am legally and ethically responsible for his well-being. If he's not willing to listen to me, I have no ability to protect him.
I would probably see this kiddo the same way you do- his parents are the problem, he's just unfortunate enough not to know better (and I can empathize with that because that was me as a kid). So, it might be possible for you to earn his trust- be his friend, but still be firm about whatever rules you think are appropriate for your household. If he doesn't like it, he knows where the door is. Sooner or later, he'll probably learn that he's welcome at your place when he follows your household rules, and when he accepts your boundaries about when other kids are allowed over, and when they're not (especially if you emphasize that these rules aren't specifically for him, but for every child- you are not targeting him even though it's possible that his family is encouraging him to think of himself as a social pariah).
BTW, it doesn't seem like his parents really care about what other parents might be teaching him, so I'd feel free to indoctrinate him with whatever boundaries you feel are appropriate- it's not like he's receiving this education from his parents.