From that article, "digit" should be spelled "dig-it", its how its pronounced.
Dig-its were the guys who would step over everyone to take credit for something they didn't do. Or, they would become the self-nominated "morals cop" during an underway or port call.
To whit-
"COB, COB!! I just saw a group of guys playing acey deucy in crew's mess..for MONEY!! I jotted down their names in case you'd like to write them up."
The name comes from saying "Hey, I dig it!" when talking about some new catch-22 changes the brass passed down from above. As in, "Hey, I heard the Pentagon is cutting our pay in half to cover our mandatory sterilization operations!"
"Hey, I dig it!"