DRK/MNK is fun! You get to Chi Blast out of your weapon! lol

Though it is overlooked, DRK has always had the potential to be a good tank. The damage output and hate-generating abilities make it quite easy to hold hate, you just have to get around the squishyness of the job (as Rezeak has explained here)

I see it this way mostly: Inside Abyssea you will probably tank as /mnk (except on stuff like Karkadann and Iron Giants) due to the extreme counter rate from certain atmas+Counterstance, as well as the high HP. Outside, you are probably better off as /NIN or not tanking at all XD

That being said, I tanked a lot of the Nyzul bosses, Salvage stuff, as well as the MMM bosses (75-80 cap) as DRK/NIN with little problems.