DDJ 1000 Compatibility with RMX 1000

Yes, but only in these configurations:

1) Between an external input device and the DDJ (and it would only affect that unit).

2) Post-master - connecting the outputs from the DDJ to the input of the RMX, then out to your speakers or recording device. That will only affect the master signal and as it's post-controller, there's no headphone cueing of the RMX through the DDJ.