I've done this duo 4 times from 1 to max level. It's great. The shaman can tank, but doesn't have to. Depending on gear, mobs, etc. either can tank just fine. Another thing worth noting, if rogue is tanking he can evade when backstab is off cooldown. That will maximize dps and let the shaman save health for cannibalize.
Also worth mentioning, this type of duo really shines for a troll or iksar. The innate regen is worth it. For even shorter downtime, the rogue can bandage while hidden.
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