Spirits are, in general, vulnerable to Stun damage (although, of course, gel ammo would have to get past the Immunity). That is, unlike drones, I can principally deal damage to a spirit using gel, can't I?
EDIT: The barrier itself is also invulnerable to Stun damage, right?
Damn, I really shouldn't have loaded gel. Also, deckers are not really, really useful when there is nothing to hack -.-