It appears the new trucks running DEF are doing so reliably. As far as the pre-Def Rams go, 07.5' to 12', not a chance if it were my money. I had a 09' and the thing was a shop queen, EGR replaced a couple times, check engine lights, turbo cleaned twice and replaced once all within 12,000 miles. My advice to him would be to look for a 06' pre 07.5' 5.9. Just get ready to pay a premium.
Did I mention the oil contamination from diesel fuel do to regens? Nothing better than watching your fuel diluted engine oil grow on the dipstick each time you check it.
Did I mention how much I love the EPA...:B?