Ah, Stone Vigil - remember that one.
This is one of dungeons where tank is the most important factor of finishing it without wipes. If dps keep getting aggro and is hitting the same mob as tank (not randomly pulling mobs) then it is tank's fault and you should not be too worried about it.
Of course there are always tanks who say "The heal let me die", but in most cases it is due to bad pull or bad place where to stand.
Don't sleep mobs - just do it for mobs who have aggroed on you. It is not your job to sleep mobs and honestly nobody can expect you to do it as casting time is too long and you can only sleep one target at the time (blackmage can sleep more).

So anyways - don't be discouraged to play with WHM. Just watch your threat level and always remember - healing yourself comes first, then tank and then dps