If you find a hidden system (or enter any named system that is) you will be able to see all planets suns etc in it, plus any stations that don't have ECM. If you cannot see any either it is only a deep space system (does it have a name in the co-ords your at?) or there is a bug with the cockpit scanner bit.
Hidden systems are known by quite a large group of people and are all most likely claimed. If you bought all the hidden system coords off CPM all it's good for is visiting and sightseeing. You won't find any unclaimed planets.