Very good question. I do know someone who soaped into a TRI after going unmatched... They likened it to a year of getting paid to be an intern, but time that would not be honored by any combined ACGME residency program. This person just finished their intern year in the ACGME program where they successfully matched during their TRI, a grand total of two intern years. Sure it might transition a resident into some specialties but not what this person wanted to do.
I would assume that since they're now called ACGME TYs they would be honored, but that explains why the current residents are all DOs. Consider emailing some residents there to get the full scoop.