I’m using 4.11.2 with DK2 running Oculus 1.5.
At first, the VR preview screen in UE was black and my rift was the gray default. I read somewhere that you may have to look 90 degrees right or left and sure enough I looked right and there was some text. After I clicked the controller A button my preview works from then on out. I will say it took me a few attempts to figure that out but once you do there is no issues. Also make sure in Settings > General you set Unknown Sources to enabled.