Archerfish will eat Sailfin molly fry - in fact, they'll eat any fish small enough to fit into their mouths.
However, in the wild, they are known to have more invertebrates in their diet, particularly insects and other athropods from the overhanging branches above.
What I'm saying is that it is OK to feed fish to your Archers, but be sure to also feed some insects (such as crickets, flies etc) as well.