I have seen DPS rip aggro off the tanks before in previous expansion times for dungeons. The aggro dumps helped, but the SAM were still catching back up mid fight with a more freshly geared tank in a leveling roulette. The SAM players were asking for a secondary threat dump to something like Third Eye -> Merciful Eyes. Even then, this suggestion might not have helped too much because the boss might still rotate to the SAM with a cleave casting.