I play both Irish tenor banjo and clawhammer. I've never tried flatpicking the 5-string. I tend to have a heavy touch with a flatpick and I don't think I could make the adjustment to the fairly light strings. I think, if I saw the pictures correctly, that the banjo player for the Squirrel Nut Zippers played chords on a five-string. At the turn of the century (last one that is) playing chords with a plectrum was fairly common, until makers dropped the fifth string and had 4-string, plectrum banjos with the 5-string scale. Recently I looked at an Orpeum 5-string that had been converted to a plectrum, with the 5th string bump shaved off, but then reconverted to a 5-string (decided on a Gibson longneck instead). I have a couple 17 fret tenors that I think are a lot of fun. The short scale makes them very easy to move with. In short, it should be possible and even work well. I'd use a fairly soft nylon pick to start and play with what you like after that.

Enjoy,

David