I changed oil in my '04.5 Cummins every 7500 miles as I didn't drive in dusty conditions very often.
Sold the truck at 168,000 miles.
My 2013 6.7 Cummins oil got changed every 15,000 miles as it lived a pretty easy life. Sold that one at 70K miles as I didn't need a 3/4 ton anymore.

My little 3.0L Ram diesel gets oil changed at 10K miles with T6 Rosmella synthetic. No oil related issues but it's still fairly new.

Unless you don't regularly change air filters and run your diesel hard and put it away wet, I haven't seen a need to shorten oil change intervals. If you read the owner's manual, you see what they call severe service and base your oil change mileage on that. I'd go so far as stating that it's throwing money away changing oil every 3000 miles.

Buy a 4-2-1 filter pack from Geno's and buy oil from Fleet Farm when it's on sale and you're set.

For the OP's question, the oil never gets up to temp if you don't drive a diesel so idling it once a month is more harmful than not running it at all.