Their reasoning is understandable, I wouldn't be as concerned since you replaced the shaft 6-8 years ago, If they want pics of the new shaft I would just pull it and rattle can it a flat black or silver and put a new Mopar PN sticker on it.
My shaft is still OEM at 255K, but I rarely lock my hubs and drive at highway or road speeds with it. Not worth the risk at 20years old.
I agree with Ozy, shafts are no small expense, I was looking around and saw them around the 4-500.00 range.
Another point to consider, someone who wheels in theirs may be able to add light; but how often do these TCs fail with a cause unrelated to the shafts? A stipulation from a rebuilder like that on their warranty would absolve them the bulk of liability for their product if that is the highest cause of failure.