Some demons use Shadow magic mainly the Nathrezim, or Dreadlords as most call them.
sure, it might work, but then I don't know. they are condensed, shaped forms of shadow/void so when they got struck by the shadow bolt they might actually disperse as you have said, but it would still leave the pool the same, so either they disperse permanently or just temperoraily and reform as greater being of shadow(containing our bolt's energy)
Demon Hunters use a touch of Shadow magic in their abilities because they're partial demons, and demons have always dabbled in Shadow as well as Fel and Fire. While mostly they rely on raw Fel or chaos energies, the Vengeance specialization uses a good deal of Fire as well.
"We're more of the love, blood, and rhetoric school. Well, we can do you blood and love without the rhetoric, and we can do you blood and rhetoric without the love, and we can do you all three concurrent or consecutive. But we can't give you love and rhetoric without the blood. Blood is compulsory. They're all blood, you see." ― Tom Stoppard, Rosencrantz and Guildenstern are Dead