Just to clarify, since there's some incorrect assumptions being made in this thread: there's really no distinction between "device syncing" and "saved game backup" - it's the same thing. In either case, all that's happening is that the app is saving some relevant data about the user's progress on Apple's servers, and then loading it the next time the app is booted - whether its on a new device, or the same device after the app has been deleted doesn't matter, the action is the same. So Zombieville USA 2, and any other app that successfully syncs across multiple devices, should be included among the list (I actually just tested it to make sure I'm not losing my mind - my ZV2 save gets retained after deleting the app).
That said, you won't necessarily see the app in your list of "documents/data". Without getting into excrutiating detail, there's a couple different ways that apps can store their data on the cloud, and only one of them shows up in your device's storage & backup details. Generally apps that store a very small amount of data won't show up there, and will be essentially invisible to you.