Not completely sure if we are talking about low level dungeons, or high level dungeons, but I was healing RFK two days ago, and after the first pull the tank asked if he could use a 2H.
Group consisted of:
The warrior asked if he could use a 2H for now, and I said sure. I assumed he meant unless he needed a shield at some point. I had him chain pulling as long as I was above 50% mana, and I think I only stopped to drink twice the entire instance. A couple times we accidentally pulled a patrol of 3 or so, and no one ever died. Honestly, I didn’t even notice that he took any more damage than previous tanks did with shields…
And on that note, I think one of the best tanks I’ve had so far was my cousin on his enhance shaman. Using a 1h and shield. Not sure how efficient it is for the shaman, but he held threat just fine, didn’t take too much damage and the runs were quick.
Again, it could just be because it’s low level content, and not 40+ stuff, but I’ve never had an issue. I’ve never really cared who gets aggro, or who pulls, or who stands in the fire. I also rarely keep the tank at 100% health, I usually start and stop casting until they are about 50%. If the dps is above 70% health, I don’t even bother healing them unless they are maintaining threat.
TL;DR - No mana problems healing a 2H tank around level 28-30.