The normal forum talk about stress and corpse hauling refers to the dwarf thought "Doesn't really care about anything anymore" as being the best for corpse haulers.
Take a quick look at this old forum and wiki info. This data will still be highly accurate, and it will give you perspective.The dwarf thought "Doesn't really care about anything anymore" is the highest level of "detachment". I am getting this info about "detachment" from the DT source code, which has a resources/game_data.ini file, which shows these levels of detachment:
51/level_0 = "Has experienced some tragedy"
51/level_1 = "Is getting used to tragedy"
51/level_2 = "Is a hardened individual"
51/level_3 = "Doesn't really care about anything anymore"
"Detachment" is listed in that DT file under the "facets" group, even though it is not listed in the
wiki's personality facets info, and that might help you access the value in DT.
So... if you want to use DT to find dwarfs that
are currently good for corpse hauling, build your DT formula to use the dwarf's "detachment" level.
And, if you want to use DT to find dwarfs that
will become good for corpse hauling, you want the dwarfs with skills and personality traits that reduce how much stress the dwarfs receive each time they see a dead body (discipline and stress_vulnerability, probably more...).
Because these dwarfs will receive less stress each time they see a dead body, they are more likely to survive their stress level until their detachment level increases.