The human eye does not always point visually 100% parallel during motion or at certain focus points, there is a slight deviation depending where you are looking and how far, sometimes it is very slightly cross eyed and sometimes each eye would seem to be looking outward away at different areas, and sometimes this is not visible in motion but rather during stills, which is why a single frame photograph of a face in motion can sometimes have undesirable effects due to the eyes re-adjusting at that particular frame while if you see it in motion it would look fine. This is not always the case though and the amount of deviation can be caused by many factors including age, muscle dysfunction, trauma, it is known as Exophoria. In default rig pose however it is generally a good practice to keep it parallel in order to setup the controls properly. I don’t see why this should be of any trouble to you, since if you are going to use this eye from this particular model sample, most likely you will be needing to take the eyeball out and re-position it in your custom rig however you like, and that would mean to rotate it and scale it as necessary.