Skills are level/2 + stat +5, with a possible +3 on top of that (I'm including the +5 for trained as a gimme, because I figure that anyone who wants to use the tactic is going to be trained in Intimidate).
Defenses are 10 + level/2 + stat, and in this case you get an extra +10 on top of that for being Hostile.
Seems to me that the skill, in this particular case, will generally have a pretty hard time getting through the Will defense. I agree with the "sometimes surrender makes no sense" though, and in those cases I will try to have the monsters run away or something.