Without knowing the full story, it's hard to say whether it means that "they" (whoever it is who won the Best Americana Album Grammy nomination) went on tour with other "folk and bluegrass" bands or if perhaps two bands have been nominated and they went on tour together.
Can you tell us who the bands/singers are? Can you tell us which one of them (or both) has been nominated for a Grammy?
You need to separate the two halves of the first part:
[Being] folk and bluegrass tour companions - and recording in Nashville - are the two things which have won them their nominations.