VR 3D Filming - Starter DIY setup

So, does one REALLY need fisheye lens for recording 3D video for the Rift?

The standard Gopro lens IS a fisheye lens. If you fitted it to a sensor larger than the Gopro sensor you would see the full circle image it can create. Its coverage on a larger sensor would be a full circle 170 degrees across. But on the smaller Gopro sensor with 4:3 formats it images approximately 110 by 80 degrees. Since the Oculus field of view is about 90 degrees horizontally it means you can only turn a little bit before you come to the end of the image. Which is why people generally use modified Gopros with shorter focal length fisheye lenses that show the whole 180 degree fisheye circle on the Gopro sensor -- which when processed into a perspective for the Oculus Rift (equirectangular most commonly) provides more look-around capability.