ROC/ROD is only sent by aircraft fitted with ADS-B, which includes most, but by no means all, Mode S-equipped airliners.
Among the exceptions are MD-80s, CRJs, ERJ-145s, etc.
I doubt this is true, but I can't confirm it. We get ROC/ROD from all MODE S readouts if we get anything at all. I doubt that they are all ADSB equipped, but perhaps they are.