[Gear VR] ES2 renderer and roughness map in the material ?

I am trying to add glossiness to my material with roughness map and while it should work on mobile (judging by UE4 docs), it doesn't show up in Gear VR.

Does ES2 support roughness or just diffuse/normal maps ?

If so, do I need to have HDR on? (which I would rather not do)

If ES2 doesn't support roughness, why not to support UE4's ES3.1 renderer in Oculus Mobile SDK (or other way around) since Vulkan API isn't even suitable for mobile VR yet ?

Thanks