For our attempts we had a DK tank on Stormcaller and Molgeim, the DK tank worked really well for a couple of reasons.
1. Overload - When Stormcaller started to cast Overload I poped AMS and damage was nothing didn't even bother to move.
2. Rune of Power - When Molgeim cast Rune of Power he would hit me for up to 18k, so moving him out of the buff fast was essential. I found sometimes it can be a little inconvient to move Stormcaller out of the buff and he'll go crazy with increased damage Chain Lightning on the raid. I was able to get around this thanks to either deathgripping him out of the RoP or Strangulate worked as well. Both fast and easy ways to reposition them.
3. Lightning Whirl - much like a warrior tank, DK's can interupt with Mind Freeze, I waited for Whirl and interupted. also to help interupt other casts and help the healers deathgrip and strangulate still work to interupt and reposition.