Jazz is unique in that it sort of has a deconstructionist criticism component built into it. By choosing which popular songs to reharmonize and reinterpret jazz musicians bring new interpretations or levels of depth to previously heard pieces of work. If you need an example of this just listen to My Favorite Things as performed by Julie Andrews then listen to it reinterpreted by John Coltrane. In pursuit of new source material Jazz musicians have mined everything from Nick Drake to Gershwin and back. A glaring gap that has somehow been overlooked, however, is the category often grouped together as American "roots" music. The cannon of music that includes bluegrass, early country, and popular folk songs has largely been ignored by mainstream jazz. Bill Frisell and Bela Fleck are two musicians who have proved an exception to this.
Bill Frisell came out of the ECM and New York Downtown Jazz Scenes and starting in the early 90's he started to introduce elements of that sound with traditional music. This led to colloborations with folk and bluegrass artists such as Emily Lou Harris, Jerry Douglas, and Suzanne Vega. Frisell has increasingly used countryesque motifs in both his solos and his compositions and they have become a hallmark of his style. There is a new "The Best of Bill Frisell" album that is just his interpretations of folk songs. I suggest you take a listen if you are unfamiliar. Here is a great live version of Bill playing Wildwood Flower and for those who are unfamiliar with the tune here is the Carter Family doing the same tune.
Bela Fleck first came to the public's attention as the banjo player in New Grass Revival, a group that would also launch the careers of Sam Bush and Pat Flynn. On his own he quickly strayed even further away from the NGR's progressive bluegrass with his group Bela Fleck and Flecktones by incoroporating elements of funk, jazz, classical, and rock. He lists Chick Corea as being one of his main influences and has performed with him on several occasions. The video below is from a live performance with Chick Corea and Bobby McFerrin at the Blue Note in New York. Here is a clip of the original Return to Forever group playing it in 1975. Finally, here is a video of Bela playing some traditional bluegrass with none other then Steve Martin.
As far as I know Bill Frisell and Bela Fleck have only had one recording together. It was on the 1996 album "Falling Off The Roof" by the Ginger Baker Trio. Bill Frisell was the guitarist on all the tracks and Bela Fleck guested on three. I have not heard the album but it was very well received and has been recently reissued.