Transfering Characters and Death Knights

Q u o t e:
Once the Death Knight is created it is treated the same way as every other class in regards to server/account transfers. Same thing for once created they still work even if your main is transfered away.

This information is entirely correct. Thanks, Aslandera.

To add upon what has already been said, you are able to transfer your Death Knight to another realm and the character will remain playable. With that being said, however, I recommend reviewing the following thread before transferring for the purpose of playing a Death Knight on another realm:

Q u o t e:
With the next minor content update for World of Warcraft, we will be opening up death knight character creation so that if the account you play already has a level 55 or higher character in World of Warcraft, you will be able to create a new death knight on any realm within your region. Please keep in mind that restrictions still apply to new, non-transfer realms such that death knights cannot be created on those realms until you level a character to level 55 on that realm or until transfer restrictions are removed. For any players considering creating a new death knight, we wanted to give an early heads-up, in case you wished to create a new death knight on a realm other than the one where your characters currently reside.

http://forums.worldofwarcraft.com/thread.html?topicId=14287209664&sid=1

Please let us know if you have any further questions, friend!