You'll note even FCA has the right to repair with new, used, exchanged, etc. parts. however, you should note that those catalytic converters are covered for 8 years/80,000 miles. Most aftermarket, best case, is covered for five years so essentially you're getting the same coverage. I can see why the insurance company is trying to go that route. What you need to look for, should you lose the OEM position, is to insist on CARB-compliant cats as you would not have to certify your vehicle in a lot of other states that test and inspect emissions. Texas is not one of them so not sure how far you're going to get but maybe you move a lot? I was in the military so I would have stood firm on this one.
Lastly, the new cat setup on your truck is about $1600 so I wonder what the aftermarket setup costs/their stated reimbursement? I see prices from $600 to $1000 for aftermarket replacements and surely the body shop can get a better price on OEM? I would be squeezing the aftermarket price point as much as possible and looking for the best price OEM if I needed to offset out of pocket.
Hope it all works out.