If memory serves, the only difference is if you happen to be lifeless / inanimate. You still take life drain damage (!), but the drainer will not regain hp / fatigue in the process. I seem to remember killing a (Dom2) Sacred Statue with Drain Life casts...
Rarku is nasty. Not as nasty, perhaps, as the two True Ethereal forms are of Umor, depending on just how much protection TE offers.
A Spirit Helm will offer extra lightning damage per turn; so does the shield o' shocking grasp. A Phoenix Rod will do fairly significant always-hit armor-negating fire damage via Incinerate. Frozen Heart may also help. A bodyguard of Storm Demons might also be fun.
Life drain + inanimate
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