Let me break in down for you in layman terms -
Diesels are really bad at getting little particles past the rings and those particles get into the oil unlike gassers. SO what to do - diesel oils have the ability to contain this particles in such a way that they do not harm the bearings and whatnot. NON diesel oils DO NOT have this ability. SO ALWAYS use diesel oils on diesel engines.
And as for synthetics............ they are not any slicker than conventional oils, and they don't really cost a lot more these days either. WHAT they DO is this - they flow better in cold, much better in cold, the wear on a a engine is created when you turn your key - after it is running and warmed up.... very little wear occurs.
Another synthetic advantage - it does NOT break down as fast, the base of oils is higher and more refined making it a "better" overall oil. AS the old argument has been discussed here 6,341.37 times ......... why use synthetic if I change my oil every year or 50 hours???? WELL ...... it is like this, IF synthetic "last" longer, and works better in cold start up.... why NOT use it? Way too many tests have been run to prove that it will do the little things better than conventional oils.
But... your pocketbook and your machine - treat it how you see fit!