Will a ball python eat a spotted python?

No, it won't even try, but they will compete for space (no matter how big your cage is) and possibly transmit diseases to one another. They shouldn't be kept together for these reasons.

I've seen spotteds in communal cages (with corns, actually) that were perfectly healthy. As long as both are regularly checked by a vet (and are not carriers of diseases they [respectively] are immune to) and are kept in sterile conditions, it should be okay. Make sure that one does not outdo the other in size and that your cage is large enough so that competition is minimized.