Let's say I have 1 battle.net account, and 1 main account (A). I now want to create another account (B) under the same battle.net account. Will the new account (B) allow me to create a DK without having a level 85 character in it?
I dont think it will. You need to have a level 55 or higher character on any server under that license. While the battle.net account is the same for both licenses, they are still 2 seperate WoW licenses. I have not tested this so dont take my word for it.