I guess Mutt Lange producing Shania Twain for the first time would have been considered very odd. I think they ended up getting married.
Philip Bailey of Earth, Wind and Fire said he got a lot of flak for selecting Phil Collins of Genesis to produce his second solo album. The result was excellent and a great pairing of two from different backgrounds. EWF would often feature rock elements in some of their songs and Phil Collins was a huge EWF fan who eventually used their horn section both with Genesis and his solo work.
By the way, Collins was a great producer. He also produced an album by Frida of ABBA. I Know There’s Something Going On is a GREAT song that is rocking and sounds nothing like ABBA. Listen to the drums PC plays on She’s Waiting, a song he produced for Clapton. Excellent!
I imagine people were surprised that David Bowie collaborated with the amazing Nile Rodgers on his album Let’s Dance. It only resulted in the best selling album of his career. Another great matchup.