Currently it’s impossible to have 3D UI for Gear VR without either making player cross-eyed (keeping 3D widget inside player’s bounds so it never goes through other actors or world’s geometry) or having 3D widget fall through geometry.
3D UI is critical part of mobile VR (and Gear VR in particular). Epic devs, please add such option to UE4 4.12 or 4.13 for 3D widget (or offer an alternative way of making 3D VR GUIs with UMG). Along the way please fix this bug [Gear VR] 3D widget doesn't render correctly - Rendering - Unreal Engine Forums
Thanks