Now that I know that I am dealing with a sepex motor, I gave it test #2 by hooking up the field to 12V and armature to 12V (parallel instead of series). VOILA - the motor spun right up.
Paul at EPC Corp is sending me a "field control module". Basically, it is a constant 12V supply with spike suppression that hooks up the to field to give it a constant voltage, so it will act like a series wound motor when I power the armature with my Alltrax controller (notice the massive spark in the video when I disconnect the field from my power supply - this module takes care of this so I don't fry stuff when I shut it off). Honestly, I am a bit skeptical, but he says it works. It won't have regen braking or make the motor reversible, but that's no problem. Maybe it will open doors in the future if I play around with field voltage on a separate rheostat of some sort.