Hit cap for special abilities against a skull mob is 9%. Depending on what spec the DKs are this might be enough. I forget what the number is for normal melee swings and other abilities, but you should be good with 12%.

As for the 1400 dps, I'm curious what you attack power and rotations are like. If you are going a blood self heal route then the number is reasonable, but it feels low for a standard dps build. I would expect something around 1600-1800, but I could be off since its been a while since I've been dps specced on my 80 DK.

- Souca -