According to lore, Emperor Palpatine was the one who named the Death Troopers. He did it to play into the existing rumors that the Empire once had a project to study reviving dead tissue - in other words, the in-universe Death Troopers are named after the story told out-of-universe in Death Troopers. Cyclical!
Bonus: height difference between a Stormtrooper Night Trooper and a Death Trooper Night Trooper:
Has anyone read the book? Is it any good?