i have seen pleco's in along with breeder tanks plenty of times so i would believe that they woudnt eat any of the fry at all and possibly would work wonders in to keep the aquarium clean.
I have kept small plecs in my guppy tanks with no problems. While they eat any leftover food, most algae and any dead bodies, they do poop a lot and so the tank isn't actually any cleaner.
Plecos dont eat fish poop, they make it.
I was also given a 6" goldpot pleco that had learned to slurp up small guppies. But I suspect it was underfed.
A bristlenose pleco would probably be ideal, unless you want to use the feeder tank as a growout for a proper monster plec
neither plecos, cories or autos "eat" poop... they will clean up uneaten food and dead bodies and for the most part leave the fry alone... they will all eat eggs though...
snails will eat poop, leftover food and dead fish as will ghost shrimp... the shrimp may eat a fry or two from time to time but i wouldnt worry about it...