Just for the record, tremolo isn't alien to 5-string banjo. You hear, to name one example, Pete Seeger using it from time to time; iit's described in both his book and Peggy's book, with reference to song accompaniment where the song requires something free and unmetered.

I've also heard it in Classic Banjo tunes a few times. I've never really listened to much of their stuff, but I'd be surprised if the much-lauded banjo whizkids like Bela Fleck and Tony Trischka didn't employ it from time to time.

Those Irish-style single-note triplets you don't tend to hear so much in 5-string banjo.

Mainly I guess because there tend to be strictures about the 'correct' way of playing certain banjo styles i.e. knock-brush-thumb for clawhammer; or 'minimizing playing consecutive notes on the same string' for Melodic style). But that's not to say you don't hear them. I play them using fingernails or fingerpicks, and I don't find it any more tricky than I would using a plectrum on a mandolin.