I get the impression that suicidal jihadis are taught less about sight alignment and trigger control than they are about putting the selector lever in the first position and hosing down crowds of cowering infidels.
I got to fool around quite a bit with unsighted, hand-held full-auto fire when I was in the Army. My team mates and I found out quickly that it's OK against a single target or massed individual targets up close, but that it gets exponentially less effective as distance increases. With that in mind, I think that a trained pistol shooter might be able to do good work IF he keeps his wits about him AND if the long-gunner has NOT had any real marksmanship training AND is on Full Auto. If the bad guy is on semi, then it's a very different ball game because he has at least some idea of what he's doing.
But if the bad guy is spraying and praying, then the hand-gunner might be safer at the far edges of effective pistol range (40-75m) than if he were within 20m, and closing the distance could increase the danger of the bad guy getting a lucky hit.
Okie John