I dont see why people roll 1 shammy as healer?
With a decent tank, 4 elemental shammies is more initial DPS, and overall DPS even if you have to heal from time to time.
When it comes to strategy, i actually pull with the shammies, killing 1 target before it reaches the group.
A demo roar from the druid should be more than enough to pull aggro from the rest, then swipe.
This should be enough to keep threat above the healing aggro the shamen produce.
Then just focus DPS to the next target, dont mind if the druid looses aggro, it will be dead before it reaches the shamen.

On your spec : I'd remove the points in reverberation, and go 3/3 Elemental warding and top out Unrelenting storm. On the healilng side of the tree, I'd drop 2points from Totemic focus, as it's a relative low amount of mana, considering a totem farm usually lasts 2 pulls. And put them in healing grace instead, to reduce your healing aggro even more.
With that spec and setup, your druid should only have to demo roar to keep aggro, no massive tanking, except on bosses.

Of course, its worth testing, what suits you best.. Its only 100g to find out what you prefer