In LOTR Sauron and Saruman use the services of humans in their armies:
The Two Towers - Helm's Deep:
Brazen trumpets sounded. The enemy surged forward, some against the Deeping Wall, other towards the causeway and the ramp that led up to the Hornburg-gates. There the hugest Orcs were mustered, and the wild men of the Dunland fells. A moment they hesitated and then on they came. The lightning flashed, and blazoned upon every helm and shield the ghastly hand of Isengard was seen: They reached the summit of the rock; they drove towards the gates.
The Two Towers - The Black Gate is Closed
The trumpets had not rung in challenge but in greeting. This was no assault upon the Dark Lord by the men of Gondor, risen like avenging ghosts from the graves of valour long passed away. These were Men of other race, out of the wide Eastlands, gathering to the summons of their Overlord; armies that had encamped before his Gate by night and now marched in to swell his mounting power.
So both Sauron and Saruman managed to persuade some humans to join their armies. Are there any source information that they also has some elves or dwarfs fighting for them too?