one of the biggest problems you run into with melee is the time it takes to get to your targets. 4 deathgrips would be great and it would solve a lot of the problems most melee groups face. i think a 4 DK + healer team would be very viable but having them all frost would probably be a mistake. hungering cold can be great but it's not a huge range and you dont need 4 of them. one DK unholy at least for the 13% magic damage (DK's damage is like 75% magic, thats why you need spell pen in arenas). you'll also want one of them going far enough blood to get abominations might.

the only thing you're lacking that i have is the synergy you get from all the pally auras and blessings. kings, might, devotion aura, 2 resists and a retrib aura are great but not necessary. with a lot of gear and patience that team could do very well.