I'm actually not sure. I've been wondering if it's safe to worm my whole flock, including the ducks (I use the old fashioned way-with Cayenne pepper) but no one seems to know. Hopefully someone will come along and know...
based on what i could find online, feeding peppers is not bad for bird in general. Birds do not have the receptorsfor them to register Capsicum, the chemical in the peppers that makes them taste hot to us. So birds happily eat peppers that would otherwise make us turn red, breathe heavy, and run for a glass of water/milk.