Ok, I built the package using the source from the developer's website and your spec file. Then, I downloaded and pacman clone and it worked perfectly. The supplied bsnes.desktop file in the source put a menu item in 'More Applications -> Emulators -> bsnes'.
Maybe we can get a developer to test, and then ask to be able to upload to contribs. I am just a beginner myself, so we'll need someone else to come along and take it from here.