I leveled 6x afflic locks 4x resto druids to 75 in AV from 70. I would take druids for your heals over shamans.

1. Druids have massive AoE heals with wild growth. I had 4 which made me almost immune to death but even 2 will be really nice.
2. You have all the other HoTs that can be cast on the run without stopping at all. This is important with affliction locks, you'll be running around like crazy.
3. You don't need fear protection! So you get feared..who cares? You don't need to be facing your target to dot them up and when you get feared you can't get AoE'd. Only problem will be the wild growth heals won't be as effective. Just macro up a heal for each of your toons.
4. You don't need to be in the same party ever which is a big plus.

Locks have nice survival skills even though they are clothies. As affliction you will get a portion of your damage back as healing and you can still spec to have your demons take a portion of your damage.

This group is way fun to BG and I will go back to them. I just had to level my 10x shaman team for the instant gibbing and to finish off a 10 man raiding team. I have no arena experience yet so everything I said is for BG's.