It didn't happen, at least not at IBM or Microsoft during the Joint Development
Agreement era. It would have been physically impossible.
After IBM had OS/2 to itself, all sorts of strange things went on. So, I can't
completely discount a port after that point. I would be extraordinarily surprised if IBM
had targeted DEC hardware, though.
But up until "the divorce", I can unequivocally state that no such thing
happened.
- Rob Ferguson
(Microsoft 1986-1996 and other times)