Devin,
Starters that blow up or burn up usually leave hard evidence behind which can be seen when you pull them apart. Shorted field windings sometimes leave arc tracks to the case or the armature.
Shorted commutator bars can be seen with the naked eye. I will hazard a guess that the starter itself is fine, but you have other problems. I don't know what a 'jumper box' is, but if it were me, I would clean the commutator off, reassemble the starter and test it with a known fully charged battery and some good jumper cables.
The negative cable would be attached to a clean spot on the starter and the positive cable would be touched to the lug where the starter switch connected. If it doesn't spin then, I would give it the last rites.
Stuart
