Are there any games / experiences / demos for Gear VR made with UE4 ? It seems that everything that is out there (in Oculus store) is based on Unity 
There is nothing public at this time other then the handful of VRJam prototypes.
ouch 
I wonder if it due some performance issues or just maybe engine isn’t quite ready for Gear VR. Do you know by chance?
From my understanding the engine is ready however there are a few things that the oculus market demands which are currently not implemented (volume buttons, proper “back” button as well as other important features, I have not looked into it that much as my product is no where near ready for release yet). As for performance I personally have not used Unity but from my understanding they currently have better performance. Epic had stated however that mobile improvements are currently being worked on. After viewing Gunjack ( http://m.youtube.com/watch?v=JF2aruO5jAY ) I just can not see that intro running 60 fps with the current engine so that builds confidence that mobile improvements truly are on the way.
These of course are my own personal opinions and they could be incorrect.
Ah, I see… Yeah, I am concerned about performance.
I am also concerned about a lot of stuff not yet documented (or outdated) and not exposed to Blueprints.