I've got to disagree with Bigs73. It clearly isn't needed. If you unsuccessfully unlock, you stay at the lock screen. And if you successfully unlock, you'll see your apps and wallpaper. I know this, because I've unlocked my phones many times using the fingerprint scanner in battery saver mode (and thus with no vibration).
Is the vibration an indicator of a successful unlock? Sure. Is it the only necessary indicator? No. And this it'd be great if there was an option to turn it off.