I think YouTube's policy is if you file that second dispute right back the content owners must go through the DMCA to file against you that way now. If the DMCA blocks your video you can file a counter notice and it goes from there. If it is a false claim the DMCA are the ones who will catch it right away and this will often deter the false claimants from pursuing as they are committing fraud at that point (attempting to claim copyrighted material is theirs when it isn't).
Edit: Another way to get the fake claimant removed is to get a hold of the real copyright owner who gave you permission to post the content and have them remove it themselves.
Don't quote me on this. I'm not 100% on the legal here.
As for an MCN, this sometimes stops the fake people from making claims against you as they can see you're behind an MCN wall but it doesn't necessarily stop it either. I also know that most MCN's don't offer any kind of copyright protection you're looking for unless you are a managed partner. When you join an MCN you are an affiliate until you become larger so if you get hit by that content ID it's still up to you to deal with it. The only benefit is it might deter people from trying in the first place, which is good I suppose
