Wikipedia corroborates Commodore licensing Amiga technology in exchange for REXX, but it doesn't say whether any of the AOS code actually made it into OS/2 or not. In any case, certainly Microsoft was involved.
IIRC it was GUI technology that IBM licensed from CBM for OS/2.
On a related note, I believe Sun licensed the Autoconfig technology from CBM for use in their SPARC machines.