Official comment
Unfortunately there is no Pro DJ Link in performance mode, however with Ableton Link, you are able to connect other software or devices such as the DJS-1000.
For the most simplistic way of getting the DJS-1000 to synchronize with rekordbox in performance mode, enable Ableton Link in rekordbox, then use the Link to MIDI app on an iPhone or iPad, which is then connected as a USB-MIDI source to the DJS (the camera kit adapter is required since it needs to connect as a host device). Everything works beautifully that way.
The other option requires use of Ableton Live as the bridge between rekordbox and the MIDI-over-USB connection to the DJS-1000, but not everyone has a licence for Live, and the previous method is significantly cheaper.