I'm not sure about the feather duster. but they will most likely pick on the shrimp. I have a hawkfish and it killed 2 shrimp. triggers are probably even worse with inverts.
my humu trigger ate both of my shrimp. i had a large fire shrimp and a cleaner shrimp. they all got along for the first week they were together, then I guess my trigger got hungry in the middle of the night and ate them both.