I could see it being hard to aim at them accurately enough to hit, iirc the CIWS systems are radar aimed for missle defense. Depends what kind of UAV we're talk

I could see it being hard to aim at them accurately enough to hit, iirc the CIWS systems are radar aimed for missle defense. Depends what kind of UAV we're talking about an antipersonnel UAV could probably present a small enough radar signature.