Does Martin Rotsey ever sing?
He gets close to the mic in the live situation on rare occasions
but I don’t think he has ever sung on an album.
Does Peter Garrett ever play instruments?
Yes, he has played harmonica on several recordings, and has been
seen and photographed playing guitar live. He's also been known
to have messed around on the keyboards live.
Do any other members sing leads?
Yes, Rob Hirst sings leads to a number of songs including When
the Generals Talk and Koscziusko, and Jim Moginie sings leads on
Smash the Wobbleboard.
Are there any regular non-Midnight Oil members who join the
band to play live?
Trombonist Glad Reed has joined the band a couple of times.
Charlie McMahon from Gondwanaland has played didj on stage quite
a few times.
Who sings backing vocals on the studio version of One
Country?
Those vocals were sung by Bones Hillman.
Who were the brass band in Bakerman?
The band was a high-school brass band from a local Japanese
school in Tokyo where the album was recorded.
Who writes Midnight Oil's songs?
The main contributors to the songwriting process are Rob Hirst,
Jim Moginie, and to a lesser extent Peter Garrett. Other members
have contributed at times but not so much as the others.
Who is Jeremy Smith?
Jeremy Smith is a member of Hunters and Collectors. He
played on the albums Diesel
and Dust 
(The Dead Heart, Whoah, Bullroarer,
Sell My Soul, Sometimes) and Blue Sky Mining . He is also credited for live performances on
the Scream In Blue album.