The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
16. On account of his activity there also no contradiction exists.
There is no contradiction, as the same Yama is admitted to act as chief ruler in those seven hells. Of Kitragupta and others Smriti merely speaks as superintendents employed by Yama.