Vibrate on notification in Silent Mode
It's under the app's discretion whether to alert the user with vibration when silent mode is enabled. You can contact the app developer's through the link on the App Store page.

For notifications from apps like Fallout Shelter, I like the fact that the notification doesn't cause a vibration as its there when I next check the lock screen and I regard those notifications as less important (I don't need to be interrupted for those kinds of notifications) although I agree there should be an option to enable/disable this by the user. This would have to be something implemented within the specific app.