Dehydrogenase of the (R,S)-sulfolactate degradation pathway that only acts on the (S)-enantiomer of 3-sulfolactate. Together with ComC, provides a racemase system that converts (2S)-3-sulfolactate to (2R)-3-sulfolactate, which is degraded further by (2R)-sulfolactate sulfo-lyase. Specific for NAD. Also able to form sulfolactate from sulfopyruvate. (2S)-3-sulfolactate + NAD(+) = 3-sulfopyruvate + H(+) + NADH Belongs to the D-isomer specific 2-hydroxyacid dehydrogenase family.