I started off with an awesome tank pet(scorpid) then switched to a wolf(pure dps). I tested both and determined wolf was better because he killed faster and neither him nor the scorpid ever died anyway because the BM talent tree is badass like that. Yes even with multipull enabled.
Any pet with Tenacity if better if you have a CC with multi pulling. A turtle can tank 4 to 5 at a time fine.
I have tanked up to 7 with minimal deaths with a wolf(fps said he has done up to 12 with a tenacity pet), I very much understand the idea behind having a pet with tenacity(tank pet) when using multipull, but because we are specd BM, it just isnt that crucial(depending on the talents you give yourself and your pet).