From other sources I've read that EV doesn't split like exp. However, if I have pokemon X out, defeat NPC trainers pokemon Z and he summons another one, I retreat X and summon Y and win... BOTH X and Y of them get the EV? I just screwed up X's EV build because this happened, luckily it's early on so not a big loss but it'll take time to find another one with a good nature.