Missing the point
While amusing to ponder, the research misses the point somewhat. There is nothing "secure" about the message itself. Security is provided by the method used to send/receive the message. While there are no doubt systems somewhere that still send such data in the clear, all EDI systems I have worked with in recent years use some kind of secure protocol for communications.
As for that "easily hackable" UNT segment. It was never intended as a precaution against intentional manipulation, but simply as a check-sum against communications problems, back in the days where everything was done via modem, and partial transmission of messages was possible should problems occur.