I've 6-boxed a bear shaman to 52 with a DK tank - it is a great combo in my experience. I've 3-boxed a discple to 25 or so with a pally tank and had some aggro issues on the disciple. My 6-box team with a disciple and a DK (better AE aggro than the pally) is only level 10, so it's a bit early to tell.

The problem with evac in VG is it can and does leave people behind. I used it a bit when I had 3 evaccers in the group, mostly if I managed to make a huge overpull and saw no way to survive. I think a better option is to have someone in the group who can either FD or escape combat and make sure you have the items that healers make which allows anyone to rez the healer.