Yes, its quite possible i play 4 shamans, done almost every heroic.
Only real hard HCs with 4 shamans is Black Morass, Arcatraz (this is OMFG hard), Mechanar, Shattered Halls... Ive never actually tried Murmur in Shadow Labyrinth, but ive heard he is pretty hard
The rest should be doable, just go in PvP gear for armor and HP