Hmm, I dunno, I haven't tried duo'ng it, but it sounds like fun.
The only thing about that particular NM is killing him before his -gas kill you.
RDM/WHM and NIN/WAR (BLU/NIN?) seems like a better combo to me if the RDM is good enough to sleep the weaker mobs inside fast enough (or chain sleep em), because that way you'd have a much easier time dealing with -gas.
Because he seems to waste too much time casting you don't have to worry much about melee damage, just focus on minimizing damage from his spells and/or cast the proper Barspell on long recast spells.
If you have a good sleeper there wont be many troubles with the mobs inside. But dealing enough damage to the NM is where the problem could be. I can think on many job combo duos that could deal such damage in that little amount of time, so it would be a matter of trying it out.
Unless you pull the mob near zone that is.
