The Fiat motor of course is dictated by the new owner. By comparison, the Cummins engine is developed and certified by Cummins. So for Dodge, they will basically be putting 2010 style emissions on the VM engine which has never had any of it, except perhaps an "optional" dpf. That is going to be a fun project. Last time they wanted to do that, it didn't pan out and they canceled the engine.
Dodge has not had to figure this out by themselves in the past, since Cummins was always the "big brother" given that Cummins had sole responsibility for emissions compliance on all the bigger trucks that their 6 cylinder engine (and larger) went into. On the other hand, Ford had to recently develop their own engine and deal with the full spectrum of emission control, and it is pretty obvious to anyone who owns a 2007-2009 superduty how much better a job they did on the 2010 model than Navistar (although it has to be pretty hard to do a more sloppy job than what you get from a company that operates out of Chicago)