In many leading DDD projects, especially MVC style, I see the UI using display objects that mirror domain entities, rather than using those domain objects directly. This style is obviously for decoupling and separation of concerns, and I personally prefer this style.

But what I'm not sure of, is whether this a strict tenet of DDD, or whether this is more just different developers' interpretation of it. 

Can you use your domain objects directly in the UI, and still be following the DDD methodology in that act?

Or is it a DDD best practice to always use display objects?

Note: While I mention MVC, I'm really interested in whether display objects must be used in almost all DDD compatible UI patterns in a DDD project.