Depending of the theory we would like to consider, as the ISIS is based on a religious moral he would be against it. As the death of god is one of the mayors points in his moral thesis, but if we take into consideration the Übermensch theory we can into a extent consider that ISIS liders are some kind of supermen going against the predisposed moral of western societies. But this moral is not trully orginal and created on basis of an own break with the predisposed moral of the common people, it is given by God, this will inmediatly put Nietzsche against ISIS as they don't accept the violence and nonsense (nihilism) of life and they hide themselves into their belives in order not to face this cruel reality.