As a regularly paid session musician in the Dublin area and also a member of the local Comhaltas branch (where, in fact, traditional guitar backing is not only supported but taught) I have to straddle the fence a bit on this one. There are times, at the sessions I am hosting, that the guitars and bodhrans can become overwhelming. I've managed to institute an "unspoken"(and it should NEVER have to be spoken) that one guitar backing at a time is adequate. The same with bodhrans. The truly good bodhran players will put their instrument down when they see another one being played. There is a space in all sessions for all instruments...the secret is finding the space and making it work..and making sure no one else is in that space at the same time. Pretty much the same as lining up at the check-out in the supermarket.
I am pleased to say that I am often requested...sometimes during the tunes by seasoned players...to pick up my guitar and come along. There is a percussive excitement that a truly good backer can add to a tune...and I consider myself now, thanks to the graciousness and warm reception of trad.players...to be a truly good backer.
Before anyone jumps to the conclusion that I may be a myopic guitar player with a vivid imagination..I haste to add that I also play mandolin, whistle and a bit of concertina.
I will add that it has been my experience in learning trad. backing accompaniment...I had to learn entirely different methods than the standard rhythm of mainstreet guitar playing. The accents are in entirely different places...the spaces to be filled and the spaces to vacate are difficult to find at first..but once found become as natural as breathing.