Not sure what the outcome would be but they constantly eat what ever is floating in the water column. I feed mine a mix of spirulina powder and activated yeast. Also, snails require calcium as so do the daphnia. Snails will use up most of the calcium in the water for their shells and leave the daphnia with not enough for their own carapace. I read that daphnia tend to do poorly with snails because of this... Again, just something I read.
Daphnia are cheap and you only need a small number of them to get a colony started so why not experiment!