When I launch my app on the iPhone X simulator, the Game Center badge is over the notch. I've got the Storyboard to use the safe area layout guides and the rest of my app is displaying properly.
Unfortunately Apple doesn't provide a public API to manipulate the Game Center banner, but banner notifications currently clip in a similar way on the iPhone X so it's likely that Apple will fix any notch-overlap issues in a coming build. It's also worth noting that there's no mention of this issue anywhere in the Xcode 9 Release Notes or the iOS 11 GM Seed Release Notes. They are probably aware, but it doesn't hurt to submit a radar!