Yep, and teaching the tank, even a little will help them more in the long run than sleeping a couple of enemies.
For me to be pushed healing in a dungeon, it has to be more than min ilvl. I have to be min and people have to be doing foolish stuff. Tank pulling big with non aoe classes, when they can hold hate, and dps is super slow. Tbh, I can't think of a time when it (sleep) was really useful to me as far as damage mitigation.
Like I said, Holy helps for dpsing longer, and I'll heavy things like True Heart, but it's not a must.