Clearly I'm going against the grain on this one... but I don't really understand your concern. What do you think will happen at a a play date with parents you, "don't really KNOW" that would be any different from parents you THINK you know.
The kids will play, they may argue or yell at one another, or they may not. They might even have a physical altercation and the other parents will have to break it up. They could eat a snack you disapprove of, or maybe they'll watch TV. But in the end, does it really matter? They're kids. If something happens that you don't approve of, you can weigh the consequences and if necessary, decide to call the parents to talk about it later.
If you want your son to be more social don't hold him back by creating false barriers. What are you afraid of? You're not ever going to KNOW all the people who enter his life. If you're truly worried, focus on teaching your son what you think is acceptable behavior -- no touching p****** p****, we don't hit one another, we don't yell at one another, call 911 if you ever feel threatened, call home if you're not having fun, etc. -- and then let him be a kid.