Johnny Winter on bass with Jon Paris on guitar playing "Rockabilly Boogie" (1979): http://youtube.com/watch?v=bRd0M41Tw3M Johnny used to be a heck of a finger-picker, and started playing guitar in the Merle Travis/Chet Atkins style, so I guess he has a pretty good knowledge of bass lines from his guitar playing.
No, JW used a thumb pick, and you can clearly see it toward the end when they're playing each other's instruments.