Go ahead and re-install the most recent version of the Game Capture software, found here: http://www.elgato.com/gaming/download. You may also want to try running OBS as admin.Yes I have I was streaming using it before I tried setting it up in OBS. I can stream using my monitor capture Scene, but the new Pro won't show up to add. Maybe try reinstalling OBS?
The now default 64bit Elgato software download includes the 32bit drivers as well, so it should still work.Also, are you running OBS 32-bit or 64-bit? Last I knew, the default Elgato software only provided 32-bit support; the 64-bit was a separate software package. If you're running 64-bit OBS, and only have the 32-bit Elgato software running, it would not appear on the list.