When I was there is June, there were two lounges; one Thai (and affiliates) and the other was a "pay to access one".
Returning in November, there had been some departure lounge changes, and the paid one was gone (the kiosk and smoking area was smaller etc etc) with only the Thai one remaining.
It was nothing special though, so I wouldn't be concerned. I can't remember if Jetstar was allowed acess anyway; I was travelling on Dragonair. Note Jetstar has some very very cheap fares on sale today for starclass SYD-HKT.