That reminds me... I am yet to try and take an adventurer out in the middle of the night, alone, to deliberately induce a bogeymen attack - and then lead the bogeymen into a camp full of angry bandits or the lair of some fearsome megabeast. Given their skill, they'd fair a reasonable chance of emptying the site.
I haven't tried this since 0.31, but boogeymen ignore all other creatures, and all other creatures ignore boogeymen. Someone took some boogeymen on a trip through a city into the market square, and the merchants were still hawking wares at the adventurer while the boogeymen were chasing them. The merchants were totally fine.
Again, it's an isolated ruleset that ignores the "physics" of every other portion of the game.
Ghosts are considerably harder to weaponize. Can all labours be utilized by ghosts, or is it constrained to fishing and animal training? Ghost haulers/medics could have vast practical uses (though their attempts to drag Dwarves through solid walls would be traumatizing) while ghost siege engineers and miners could be potentially devastating to attacking foes.
Most labors can be used by dwarves, as far as I know, but they're restricted to areas they liked in life. This usually means going to the same workshop over and over if they're that type of dwarf. Haulers wouldn't work, since hauling isn't a skilled labor that triggers specific preferences, and it would probably only work if it was only moving stuff from the same workshop to the same stockpile, anyway. A ghost carpenter
might be capable of still producing wood beds over and over, though. I'm not sure whether it would care about your orders, though, but the ghost tamer thing implies it would.
Your best bet of weaponizing a ghost is to use the aquatic taming trick to train some warshark tanks to dump enemies into.