A potential blowout is actually why I include Ober.
In the playoffs, the hook on starters gets shorter. If Lopez or Gray were to give up four runs in 2.2 innings, for example, you almost have to get Stewart in to put out the fire and then try to get 3-4 innings from someone like Ober to get back on track for the next day's game.
Yeah, I know, Varland, but what if he's getting hit as well? Or what if he goes two innings in the Game 1 win and isn't available in the fourth inning of Game 2?
I don't know what the pecking order is, but whatever it is, I think you drop the No. 4 starter from the Wild Card roster so that he can start Game 1 of the next round, and you have the No. 5 guy on the roster for blowout circumstances.
Remember as well that the Manfred Man rules disappear in the playoffs, so there's a much greater likelihood of a long extra-inning game where that No. 5 starter comes in handy.