At the very least, WIHH Jakarta, WIPP Palembang, WIIS Semarang, WARR Surabya have coverage in this area as well as some Malaysian stations. Whilst the Indonesian AIP is not currently available on line in English, a quick look at the source data being used by FlightRadar 24 will confirm this assertion - and you will also find a strange radar called TEST1 in operation too - who knows where that one is located.
The TEST1 radar is I think shown as T-EST1, and as far as I know it's actually just an ESTimated (by FR24) position, not an actual receiver. Also, those radar identifiers on FR24 are just to tell you the closest airport to the receiver being used as the source, it doesn't indicate any other connection with the airport or any ATC radar network.