Is hertog the same as the name Hartog?

Probably, as it's a Dutch name. Cf. German Herzog is the same as Dutch hertog, both of which mean literally 'army-leader': Heer 'army' and ziehen 'to draw, pull': German Zug 'train', English tug, tow, Latin dux, ducis, 'leader' (whence English duke): all from PIE *deuk- 'to lead' (link).

Ceci n'est pas un seing.