We did a 10-man DK premade in Warsong a little over a month ago. Can do it with Demon Hunters as well. In order for this to happen you need a level 10-19 character in a group with any higher level character, then queue as a group. Once in queue, all the higher level characters will be locked into the bracket of the lowest level character in the group (10-19), even if that low level player leaves the group.
To get 10 DK's into Warsong at the same time we split into 3 groups.
Group 1: 4x DKs, 1x level 19
Group 2: 4x DKs, 1x level 19
Group 3: 2x Dks, 1x level 19
Countdown and sync queues between the groups, once in queue have the 19s leave the party and voila, if your groups sync, you'll have your 10 man DK premade in the 10-19 bracket.