Definitely viable, but against decent arena teams you need to be quick and so does your healer because you do die fast. I tried some rsham-mage-sp. I used 600 resil and still noticed i could drop fast. Overall a very good comp though.
I also briefly ran rsham - sp in 2s but get ready for some long games against decent teams. Even with synapse, unless you're running full PvE gear (not advisable in 2s) you're gonna have just a bit too little damage to get the kill and only get close. It helps if your shaman has tazik but still. Ran into r-sham - boomkin, had a 45 min game and thats the last time i played that comp.