Aham!
I just converted my scene from VRay and the skyportals stand there.
Here is the end of raw render, but if you see there in the mirror the light overexposed.
I'd used only Corona Sun, here is my setups for skyportal and sun, and there is the result...The environment tab was empty. Just simple worked, but I had fixed the materials.
I have only the Alpha5, and I loaded in a week ago...But, I always trying. Specialy the materials "section" :).
If, it's not working for you, sorry but I don't have a better idea...