Great thread. Love this stuff.
It seems out of place, but rocker Joe Walsh produced Dan Fogelberg's second album, "Souvenirs." This was in Walsh's pre-Eagle days, but Don Henley, Glenn Frey and Randy Meisner all make appearances on the album, as does Gerry Beckley from America and Graham Nash.
This was back in the early days of the LA country rock movement and there was a lot of collaboration, especially among Irving Azoff's clients. The Eagles show up on a lot of Fogelberg's early albums, along with David Lindley from Jackson Browne's band, several members of Jimmy Buffett's Coral Reefer Band, J.D. Souther, etc., etc.