Disregarding exactly how difficult it is to actually Baton Pass a Substitute with either Jolteon or Ninjask in DP, considering Skarmory completely eliminates the latter and basically any Pokemon glaring at Jolteon will break its Substitute, I have to say I agree with Jump in that Petaya Jolteon is gimmicky.
I disagree with putting anything other Leftovers on a Pokemon Baton Passing Substitutes.
Jolteon, Ninjask, and even possibly Vaporeon (though the Petaya Berry Vaporeon I saw was a one time thing, lol) should all carry Leftovers for that vital fifth Substitute.
The best case scenario for the Petaya Jolteon that I can assume is that late game you manage to switch in <50% Jolteon on a 60% Water / Flyer that is vital to the opponent's strategy, and he switches to a non Phazer while you Substitute, and for some reason can't break your Substitute, and...see just how impractical this is?
I'm not a fan of absolute or limiting statements, and while I'm sure Petaya Jolteon has assisted you once or twice in a battle, I can confidently state that Leftovers Substitute and the extra Substitute it nets you (especially if something common like Stealth Rock is in play) is more useful on average than Petaya Substitute.
Though honestly, why would you guys even bother Substitute Passing with Jolteon? If you want a free switch type move, U-turn does it a lot more efficiently, and if you really want a Substitute Passer, I'd give my support to Vaporeon or even Drifblim way before Jolteon.