Pull the various enemies into the fort; they make short work of each other.

You cannot do that. If there are dvergr around (and their ward is still intact?) they will aggro if you damage them or their property.

If an enemy such as gjall has destroyed structures or containers belonging to dvergr, the loose loot on the ground is free for the taking.

You likely won't even need to actively lure gjall to kill dvergr. It's almost inevitable to happen naturally unless there are multiple high level dvergr (especially mages and healers) guarding a tower. The mining/quarrying camps are much more vulnerable and they too often contain a box for extractor.

You can use refined eitr to destroy the ward, just throw a bunch near it and wait. Once the ward is down, you can break whatever.

Thanks for the tips! This tower has about 7 of them...4 mages and 3 rogues.