hydroids only kill pods and plankton they might irritate coral but they are hard to keep alive in aquaria. i managed to get a few in my tank that i collected if i decide to buy a pygmy angel they are good live food
the eggs, probably not. Snails lay them in a nice flow to keep algae growth off of them. I usually just scrape around them.
They could end up in a filter bag. But, there are probably nests around as well you don't see
Agree- Like collanista or other would be Columbellid snail eggs but thinking collanista. Unlike many snail eggs which do not have a high hatch rate, collanista usually do. Harmless tiny pea size snails