Another new OPC commenter, tony s, has another non-singing credited artist for us to chew over:
Herb Alpert does qualify. He got to #5 in April 1987 with "Diamonds," which was sung by Janet Jackson and Linda Keith. Most people thought it was a Janet Jackson song.
I vividly remember "Diamonds," and knew it was a Herb Alpert song, so I should have caught that one. More from tony s:
Also, in May, 1972 an Aussie group named Python Lee Jackson got to #56 with "In a Broken Dream," where they hired Rod Stewart for just that session to sing lead. Don't bother digging it up for that, though; it's an awful song.
I wonder how much it costs to hire Rod Stewart for a session.