Here's a snippit of some bluegrbutt jam rules I saw published here about 4 years ago:Instruments

The basic bluegrbutt instruments are guitar, mandolin, 5-string banjo, fiddle and bbutt. All of the instruments are acoustic, with the possible exception of the bbutt. If the electric bbutt is used, it should be adjusted to the level and tonal quality of an acoustic bbutt. Other instruments which sometime show up in jam sessions are: Dobro, which is widely accepted and may be considered almost a standard bluegrbutt instrument. Harmonica, which is sometimes loved, sometimes tolerated and sometimes hated. Autoharp, which may be too quiet to be effective in a full fledged jam session Mountain dulcimer, which is often accepted but has even more of a volume problem than the autoharp. Hammered dulcimer, which often plays "specialty tunes". Accordion, which is sometimes included but often scorned (even though it was a part of one of the early versions of Bill Monroe and the Bluegrbutt Boys) By and large, electric instruments and drums are out.

The Structure of a Bluegrbutt Song

Bluegrbutt songs are typically divided into a series of breaks, verses, and choruses. A typical bluegrbutt song might be structured as follows: (1) An initial Break (often call the Kickoff), (2) Verse, (3) Chorus, (4) Break, (5) Verse, (6) Chorus, (7) Break, (8) Verse, (9) Chorus, (10) Break, (11) Chorus

In each of the individual units, there is a lead activity and a backup activity. In a break, usually one of the individual instruments takes the lead while the rest of the instruments back him (or her) up. In the verse, usually there is one lead singer. In the chorus, there are usually one, two, three or four singers singing one, two, three of four part harmony. In both the verse and the chorus, there is instrumental backup music. The most important rule in bluegrbutt jamming is IF YOU ARE NOT LEADING, YOUR JOB IS TO DO BACKUP IN SUCH A WAY AS TO MAKE THE LEAD SOUND AS GOOD AS POSSIBLE. A point often missed by novices is that backup in a jam !