Is flying a UAV via a VR controller (e.g. Oculus) legal in the US?
According to Model Aircraft Operations one of the requirements for flying a model aircraft is:


  
  Keep the aircraft within visual line of sight at all times
  


If you are wearing a VR headset, then your visual line of sight stops at the headset screen. 

Note that the above linked page lists the "visual line of sight" as a safety guideline. However, according to Section 336, an aircraft is not considered a "model aircraft" unless it is:


  (2) flown within visual line of sight of the person operating
  the aircraft


None of the above restricts you from flying with a friend where one of you is wearing the VR headset and the other is piloting the aircraft.