I do not believe, as MTH do not supply their DCS decoders to any other competing manufacturer for installation, that you will have any luck either. You will not be able to run any other brand of control system's decoder installation with their DCS controller either. In Mike Wolf's words, "DCS is not DCC". (or any other as well). He has added DCC capability to his HO line, so he could sell into that market, but I don't know if that applies to "O" scale.
As far as MTH's Rail King brand is concerned, as it's that brand, the answer as to DCS being it's control system, would be, Yes.