The Sky Tower has not been open for several months. They have been testing it, from what I can tell, so you may have seen people riding it on test rides. But it has not been open to general park guests. There is a rope across the entrance, close to the pearl shop. If that rope is blocking the entrance it is closed, and in months I have not seen that rope removed.
AshFireGaming - when you saw people riding it, did you actually walk over and see if you could get on it? If not I have to think they were either testing it or doing something special for VIPs.