For what it's worth I found this at texasbowhunter.com (beware, knowledge gained from random discussions is to be avoided):
I used the exact same lights on my shop and if you leave that red wire out only half the lights will come on. -Jes
You might want to wait for others opinions; but I'd feel pretty safe powering the black and if only half the lights come on, hook up the red too. Also if it came with them nutted after having been installed somewhere, +1. But it'd still be nice to confirm this in the installer's manual which I can't find. (Which I see you have but it doesn't match the color scheme? so, erm... call them?)
The half inch knock-out is where you're going to install a cord relief in, and then feed the cord through it and back out the rectangle hole to wire it, then shove everything back inside and find a cover plate for it.