I was fighting bandits in the sewers when one of them went into a "cower" animation, and began screaming about how he had given up.
Given that I found his terror endearing, I deigned to spare him. I tried talking to him, to no effect. Then I tried sheathing my weapon - upon which the brigand thought he had a chance, and resumed hostilities with due haste!
Sadly, he did not offer to yield again before I slew him.
And so, the question remained unanswered: do enemies actually surrender, or was this just a clever ploy to catch me with my pants down?