So I've been using my drk a lot at events lately and I've been working on tanking as drk/nin. I've tanked all sky gods with it and proto omega so far pretty easily. Now I've been tanking HNM for several years now as pld and I've never seen a practical application of DRK tanking there beyond omg i took hate once or twice and kept shadows up.
My setup I'm working on is basically for low man man co-tanking things with a setup that is basically:
PLD/nin (tank)
Drk/nin (tank)
Brd/blm
rdm/blm
whm/sch
brd/blm
blm/rdm
blm/rdm
A setup such as that would contain enough stuns and support for most low man HNM. You would of course have two blms in a stun order while the DRK free stuns. Cerberus for example your drk could effectively stun lavaspit, sulfurous breath, gates of hades and Magma Hoplin if he was really fast.
This would in turn make you ask why not just use a second PLD? My answer to that would be that a well geared drk can contribute more damage than a second pld while still being able to keep shadows up due to stun/weaponbash etc.
Drk has access to pretty much all of the damage reduction gear pld does so it is very possible for a drk to take aegis level magic damage with fast macros so as to not be a burden on healers.
I want to say again that I'm not talking about drks who use their apocalypse on cerberus/tiamat etc and take hate from damage and then have to keep shadows up. I'm talking about purposefully tanking as drk to make low man more possible.
If anyone has any thoughts or ideas who actually have experience doing this some feed back would be nice. I'm fairly sure this isnt standard strategy for most linkshells.