I see this type of question a lot. Will animal X eat poop?
Truth is...it depends. Most aquatic animals will investigate the excrement they encounter for undigested food particles, and consume if they find something. Detrivores are efficient at extracting waste from larger/predatory animals that have less efficient digestive tracks.
But what is often meant by the question is not if an animal CAN/WILL eat poop, but if it can live off of said 'food' source, and reduce the need for cleaning by the aquariast.
And the answer there is pretty well a resounding no. Especially for snail droppings--snails are pretty good at extracting 'food', so their waste isn't really likely to support another animal. Nutrition wise...poop = poop. So. Consider that a mammal can SURVIVE by eating it's own waste for a while. But it isn't great, and eventually will result in deficiencies. So don't slack, clean up after your pets.