When I ran my hunter team before 3.1, I ran 3 apes and 1 wolf with a druid healer. They can do normal instances in northrend just fine. I used the ping pong effect from my apes aggro to make it a little more healer friendly. I did not feel my team could do heroics though as it is just too much damage for them to take. Maybe if I teamed them up with a disc priest. I do believe there was someone on these forums that is running heroics with their hunter team. I don't remember who though.

Edit: sorry totally forgot your first question. With the changes in 3.1, it might be more viable with a turtle. You'd have to play around with it. but with their 50% damage reduction they are definately a strong tank pet. I've never rolled with a turtle before. Do they still attack while their shell shield is up?