Of course they eat Corals.
Plenty if info on it all over. I tell everyone that purchases them, that they can eat Coral if they dont find enough food to their liking. I also tell everyone to cut WAY back on what they feed to the tank until they see Aiptasia gone, then increase feeding. As I have found if they get plenty of other food, they won't go for the Aiptasia. Makes perfect sense...why work for a meal and get stung, when filet mingon is falling from the sky on a regular basis.
If I add them to a tank I make sure to remove them when the Aiptasia is gone.
They are good as long as they find Aiptasia or get fed enough food. If not, then like almost any animal they will go from being a scavenger to a predator. Now usually they go for meaty Corals that eat food first, like Acans, Lobo. And open Brains. But will easily bother zoas and chalice too. I rarely have them bother SPS, but he definitely seen them eat leptos and Psammacora.
I keep some with my Acropora, and never had any issues.
Other than that, they are in their own tank as cleaners. I drop a frag or rock in there and 10 minutes later perfectly clean, absolutely no Aiptasia.
I would also add, in your situation I might double check everything else, as if there is Aiptasia still in there and you are feeding, it is unlikely that the Pepps are the ones responsible for the Lepto.