I was told lamarks were reef safe and it ate the crap out of my red dragon acro.
In the wild that eat plankton and things in the water column and will eat similar things in your tank, like Mysis and such, but they may nip at corals. This doesn't usually happen right away but it does over time.
I've had both the lamark and the swallowtail. The key is feeding your fish at least twice a day. This way they don't even think about nipping. I also have a coral beauty in my reef in addition to the swallowtail. No issues thus far. Been close to a year.