I feel like the axe is better suited for executing enemies. Its quick and effortless without being as brutal as a blunt hammer. Dont get me wrong that man deserved death but not in a way that gives Dag's companions pause.
There is no need to be so brutal that you scare your allies. Your enemies, yes, but in this insistence there was no need for that because Dag already was capable of taking care of the enemies with no problems. They are going to surrender, whether he used an axe or a hammer, so might as well use the axe.