I've been able to farm him (for Sereph crystals) in UVHM using the ledge glitch. When he does his final transformation into Pyrocaustic Pete, you can burn him down with corrosive weapons, which I would not have expected.
Solo'd with 72 commando (no OP, but dual turrets w/rockets) w/Bee. Used Twister (from the loot hunt) and Miss Moxxi's Crit to burn his shields down then just kept throwing damage at him. I've had a couple of runs at him where I never opened a single valve.