According to the tooltip, the "Healing Shout" at level 35 in the Chants spec line should heal my group for 2% of their HP (including myself). The description is basically the same as the normal healing chant "Angel's Refreshment" (also at Level 35 Chants spec).
The normal healing chant with the fixed healing value heals properly for 36 HP, the "Healing Shout" on the other hand has no effect. It fires, and goes on cooldown for 60 seconds, but does not heal me in any way.
I am leveling solo, but since the tooltip matches with the other chants I expect it to work the same way.