These canon Dark Troopers were experimental combat droids and were used during the civil war between the Rebellion and the Empire, although use of the droid troopers obviously wasn’t widespread, as any Star Wars fans who have seen the original trilogy can attest.
That said, Dark Forces is part of the Legends continuity, and Dark Troopers didn’t appear in current Star Wars canon until the Star Wars: Commander mobile game, which launched in August 2014, only to be shut down in June 2020.
Taking both the Legends origin and the canon iteration into consideration, all signs seem to point toward Moff Gideon amassing an army of droid Dark Troopers.