First off:
http://www.lightnatured.com/forum/vi...hp?f=14&t=1995
Angenie is my personal healer. She's healed me since Gruul's, now in Naxx at a casual pace. We run 3 healers in 10man (her, priest, druid) and I'm not sure about 25mans. She and I built this spec back in beta, and modified as it changed. It. Works. You can find her at:
http://www.wowarmory.com/character-s...moon&n=Angenie
She is geared to make this function wonderfully, built around one major area: Crit. She's somewhere close to 30% crit unbuffed, and recommends that as a goal for any "Sheathadins" who are wanting to make this work. It is designed to keep tanks alive when every single person is dead. I've ended up solo-tanking Patchwerk (OT-healers weren't on the ball) in 10man, and it actually went very, very well (shield wall at 5%) because of her.
She knows how to run the spec, and the Light Natured post at the top explains it better, but her tactic is to get Sheath rolling a few times, to give her breathing room. Divine plea and Judgements of the Wise ensure no mana problems, and when she's running on that, she's going to have no problems keeping the Sheath rolling.
It is a -fantastic- tank healer. It's a decent raid healer, but I'd say Beacon would out-do it. Especially for main tank fights though, Patchwerk-esque, it shines beyond reason. Her spec isn't optimized for healing, I'd recommend this:
http://talent.mmo-champion.com/?pala...h=111619060504
That is made far more for raw healing, and cuts on the solo-ability (in Genie's spec, CS, DS, etc).
TL;DR: Yes, Sheath works. See the above as to why.