Are there any dwarves and/or elves joining Sauron and/or Saruman

Question

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?

Answer 1

Well the orcs may be corrupted elves.

In The Silmarillion the wise Elves of Eressëa believed that Melkor had created the orcs before the First Age by breeding Elves he had captured and corrupted, by means of torture and mutilation.

source

Due to this, Melkor discovered the Elves before the other Valar, captured many of them, and transformed them by torture and other foul craft into Orcs.

source

Though all explanations are relayed by in-world characters who Tolkien made clear are not omniscient or always correct. In his later writings it's implied that Tolkien became dissatisfied by this origin.

And some dwarves did fight on both sides.

…All living things were divided in that day, and some of every kind, even of beasts and birds, were found in either host, save the Elves only. They alone were undivided and followed Gil-galad. Of the Dwarves few fought upon either side; but the kindred of Durin of Moria fought against Sauron.

Source: Silmarillion, Of the Rings of Power and the Third Age

Answer 2

Murphy quotes the definitive answer, which is

All living things were divided in that day, and some of every kind, even of beasts and birds, were found in either host, save the Elves only. They alone were undivided and followed Gil-galad. Of the Dwarves few fought upon either side; but the kindred of Durin of Moria fought against Sauron.

But this answer is actually slightly incomplete. Elves (and not just hypothethically-corrupted-Elf-Orcs) did serve Sauron and perhaps also Saruman. There is a reason Sauron is called the Necromancer: because the spirits of dead or faded Elves serve him:

But it would seem that in these after-days more and more of the Elves, be they of the Eldalie in origin or be they of other kinds, who linger in Middle-earth now refuse the summons of Mandos, and wander houseless in the world, unwilling to leave it and unable to inhabit it, haunting trees or springs or hidden places that once they knew. Not all of these are kindly or unstained by the Shadow. Indeed the refusal of the summons (of Namo to Mandos) is in itself a sign of taint.

It is therefore a foolish and perilous thing, besides being a wrong deed forbidden justly by the appointed Rulers of Arda, if the Living seek to commune with the Unbodied, though the houseless may desire it, especially the most unworthy among them. For the Unbodied, wandering in the world, are those who at the least have refused the door of life and remain in regret and self-pity. Some are filled with bitterness, grievance, and envy. Some were enslaved by the Dark Lord and do his work still, though he himself is gone. They will not speak truth or wisdom. To call on them is folly. To attempt to master them and to make them servants of one own's will is wickedness. Such practices are of Morgoth; and the necromancers are of the host of Sauron his servant.

(HoME, Morgoth's Ring)

Answer 3

"But they are not evil by nature, and few ever served the Enemy of free will, whatever the tales of Men may have alleged." - LOTR, appendix F. Also, of the Seven Rings: "For the Dwarves had proved untameable by this means. The only power over them that the Rings wielded was to inflame their hearts with a greed of gold and precious things... But they were made from their beginning of a kind to resist most steadfastly any domination." LOTR, appendix A.III - Durin's Folk.

So probably few if any Dwarves served Sauron, and those mostly slaves.