I waited to see if someone else jumped on the killies as dithers issue. No takers so far so I'll take a stab at it, even though I haven't much breeding experience.
Some killies are peaceful enough and habituat the upper level of the water column, two factors that one would look for in a dither. However, most killies are shy and tend to hide in the weed or dark recesses of the tank nor do they school. This, of course, are not traits of a good dither.
One of my favorite killifish, Aplocheilus lineatus is an exception as it's not shy, and it's fairly common. It can sometimes be found in your local fish store as "Golden Wonder Killie." But it's also large enough to gulp down copious amounts of fry. I have kept them with apistos with no problen, but not in a breeding situation. A slightly smaller killie that can be easily sourced from a killie nut is Epiplatys dageti. It, too, hangs near the surface and is peaceful.
There may be others as well. Lampeyes, a category of irredescent killies from Africa, do congregate in schools. But they tend to enjoy fast moving, highly oxegenated waters. Some of the smaller species mught fair well in an Apisto breeding setup, but I don't know if they'd be preditory towards the free swimming fry. Plus they are not that common. But I would add that it would be a very impressive tank!