I confirmed with a resident: there haven't been any in recent memory, but we see no evidence there is any particular reason for that. Maybe the pool of DO applicants has been small (very likely) or not as competitive (possible). I have no info on whether DOs have been offered spots and declined, interviewed and not been offered a spot, or just not been in the pool of potential interviewees.
Dr. Flannigan is right: somebody's got to be first. Ya can't know until you try, eh?