Right, but it's all about that turn 1 setup... if it takes you until turn 2 to get octillary running and octillary can only use his ability once per turn. Also having an ultra ball is better than a level ball because you want to discard junk out of your hand get get nightmarchers in the discard pile. IE, you have a shay-bae in hand, with 4 night marchers and 2 ultra balls, you can dump the night marchers in the discard and set up for a new hand. If you run level balls you can't put those in your discard and you're limiting your damage.
If you're running shay-bae you can use that ability 2-3 times on the first turn allowing you to go through most of your deck without using a supporter. If you ultra ball 4 times, you're discarding 12 cards out of your deck to make room for things you'd need on that turn. Obviously if you're going against a low-hp non-ex then you'll probably not need the shaymin but at the same time octillary wouldn't be doing you much good either because you'd have too large of a hand.
Night march tends to hold a few cards that are key (lysandre, puzzle of time, etc) so I don't see octillary helping them out as much as something like greninja where they are dumping their hand every turn.