Spell Immunity is a mage spell. The only way a cleric like Viconia could protect against Imprisonment is with Shield of the Archons, a 7th level cleric spell that will only absorb two shots, IIRC.
It's either the barbarian or the berserker enrage that will protect against imprisonment, not both. Can't remember which one off the top of my head.
(Speaking of those machine-gun Imprisonments, it's not the Imprisonment spell, but a special version called Trap the Soul, that's only cast by that person, and the difference between Trap the Soul and Imprisonment is that Trap the Soul can be cast from a distance, but you have to be up close and personal to cast Imprisonment, like you have to be with Maze.)