I didn't make the .exr, Paul Debevec did; but I understand about the directions and how to assemble the images (but my photography is not very good yet). It was confusing at first; but learned the right way.
Anyway, I almost always use them as spherical environments and don't normally attach any geometry to them. When I do that (sphere environments) the directions of the original image files are the correct ones, of course. So if the images have the right direction, the environment will too. Then the skylight can just use the environment, and all is well.
I'm not rendering w/ Poser but am always interested in HDR, so this is a very interesting thread to me.

Friends don't let friends use booleans.