Can you give him proper weapons, if so, will he use real weapons on real targets to do real damage, or do ghost wielded weapons phase right through
Sadly, it seems that you can't give ghosts equipment of any kind. In fact I believe ghosts hover through their afterlife completely butt naked, since they leave their clothes in a pile alongside their corpse when they die and never pick up any replacements. No wonder dwarves are sometimes found dead from sheer horror after seeing them.
As it turns out after some experimentation, since he's a Restless Haunt, Dakost the Friendly Ghost Speardwarf provides very little military value. He doesn't participate in any military activity except by hovering somewhere in the vicinity of his militia buddies. For some reason though he is getting
Tired when others are sparring around him, even when he doesn't do anything (that's visible in logs) himself. I'm keeping him around as a militia mascot while I try to think some purpose for him.
Once I sent his squad to loot some nearby ruins to see if he brought anything back; for some reason the rest of his squad simply froze where they were while he alone walked out from the map and disappeared from the game, never to be seen again. I savescummed after that.
I'm thinking... he could be turned into a Murderous Ghost by slabbing him and then deconstructing his slab, but would he lose his squad association in the process? I have a suspicion in that case I'd just have ordinary uncontrolled rampaging undead in my fort.