Peter, your two fiddlers sound wonderful, and I'd have loved to hear them. I remember seeing Patrick Street (who of course did have a guitarist) a number of years ago and, although it was a great concert throughout, the piece that really stood out for me was Kevin Burke's solo fiddle performance, which exhibited all kinds of subtleties and a superb grasp of dynamics.

I claim no expertise in the matter, but I have always understood that a 'pure drop' Irish session would consist mostly or only of melodic instruments, and that guitars are generally considered unnecessary. That said, prominent concert acts (Planxty, Bothy Band, Patrick Street, Hayes & Cahill) have over the years used either bouzoukis or guitars to fill out a harmonic accompaniment. I'm still not sure, though, whether this is quite what the OP was asking about!