These musicians in the Scottish and Irish traditions all sing / sang accompanying themselves with 5-string banjos - whether or not they were "long-neck" banjos, I'm not 100% sure, and stand to be corrected on that :

Ireland -
Al O'Donnell, from Dublin - see cover of his 2nd LP, if I remember correctly.
Luke Kelly of the "Dubliners" [ maybe not "long-neck" ]
Tommy Makem - and also his nephew, of the same name.

Scotland -
Iain MacIntosh
Danny Couper - still playing at our sessions in Aberdeen [ although he's defected slightly to the mandola ].
Ian Walker
John McDermott - "The Laggan"

England -
John Dunkerley - "Ian Campbell Folk Group"

Apologies in advance for my ignorance about 5-string banjo neck length, but I'm always willing to learn !