I know, but since he is a great battler and all...
It actually sounds like something Emerald would look for, since he seems to be the biggest competitive battler out of all of them (really, now, he had to beat Red in the Battle Dome to get the seventh symbol, and that's saying something).
Though, I don't even know it was intended, but Zuzu's nature is actually a desired nature for Swampert when it comes to competitive battling. -I just like giving my Mudkipz a nature that is beneficial to their Sp. Atk. stat-
All of Ruby's other Pokemon have good natures, though.
Since I totally don't want to spam the club just commenting...
Coco's nature is Quiet (like Toro's XD). Quiet means enhanced Sp. Atk. stats but lowered Speed stats. Pokemon with enhanced Sp. Atk. stats love Dry food, and Pokemon with lowered Speed stats hate Sweet food.
If it weren't for Mimi, Coco would totally be perfect for Beauty contests XD