You can definitely manipulate the camera/viewpoints pitch/roll in UDK, so I assume you must mean that it isn’t true in relation to the Rift.
I have no experience with this, as I had switched over to using the UE4 beta by stage and did not investigate UDK + Rift integration any further.
So, to correct my answer:
The camera/viewpoint system in UE4 can manipulate all three axes in relation to the Rift or any other HMD.
Relation?
Don’t think I’m using the right wording still, but hopefully you get me 
Player axes + Rift axes = final camera axes.