Dunno if you've gone yet, but we just got back from a 15 day Princess roundtrip to Hawaii.
Don't sweat the small stuff. There is no longer any dress code, despite what they may say.
In the main dining room on formal night: a guy with a Hard Rock t-shirt, Hilo Hattie beads, and military camouflage pants. Nobody said a word.
I think they only retain the concept of formal night for the photo business. Many ignore it. Smart casual? Pretty much anything short of naked.