The Earthen, Tauren, Furbolg, and other races participated in the War of the Ancients.
The Earthen under Dungard Ironcutter,
More astounding, he was made of stone, not flesh. ... "Dungard
Ironcutter, speaking for the clans of the Earthen" was all he said,
dwarves not much on conversation.
The Earthen. Malfurion made certain to remember the last. "Dwarf" was a night elven word, a derogatory one at that.
The Tauren tribes united behind Huln Highmountain, Above the harsh,
wrinkled brow a pair of treacherous-looking horns thrust ahead of the
muzzle. A tauren... ... "Huln who speaks for all the tribes gathered."
The creature lumbered forward. It resembled a bear, yet moved more
like a man. In some ways it reminded Malfurion of the twin gods, Ursoc
and Ursol, but it was clearly a primitive creature. It wore a pale,
brown loincloth and a necklace made of claws. The three-toed beastman
raised a club in one hand. The other four-fingered paw formed a fist.
The creature roared again, its tone slightly different from the first
time. "The furbolg Unng Ak says that he speaks for the packs," Rhonin
and one orc
all took part in the War of the Ancients in the timeline altered by Rhonin and company.
As the tauren did not take place in the War of the Ancients in the unaltered timeline and Huln Highmountain currently exists in the WoW timeline, it can be concluded that this is canon.
In addition, numerous unnamed races were also present.
There were others behind them, but they did not choose at this time to
From this point, it's easier to define who didn't join in the war.
Pandaria, with the Pandarens, Mogu, and Mantids, was separated from the main landmass and surrounded by mists due to the actions of Emperor Shaohao, shortly after the beginning of the War.
At the dusk of the final day, the sky was bathed in green fire, and
the very ground trembled in terror. But the Emperor was not afraid.
His mind was clear of any doubt or despair. He feasted and he sang as
the sky tore open. ... And as the Emperor's robes fluttered empty to
the ground, the land became enveloped in impenetrable mists, hidden
away from the rest of the world.
The Emperor's Burden, part 8
The Tauren trapped in Pandaria were enslaved by the Mogu, under Qiang the Merciless, and were forcibly changed into the Yaungol of today. (Chronicles I)
The Nerubians were isolated in Northrend, where they took over Tol'vir settlements. Corroborated by Zarhym on the forums.
The Qiraji were gathering forces within Ahn'Qiraj, where they worked to turn C'thun's prison into a seat of power.
The Old God would create avatars from the Silithid in its own image.
These avatars were to be known as Qiraji. Sentient and with purpose,
the Qiraji would name their creator: C'Thun was born... For many
thousands of years the Qiraji worked feverishly to build a force
capable of laying waste to the world that would betray their god. The
great fortress city of Ahn'Qiraj was created to house their growing
armies and prepare for the coming of C'Thun.
The Prophecy of C'thun, as told by Geologist Larksbane
The Vrykul in Northrend were in a hibernation initiated by Loken.
Data suggests that impetus for global combat originated with prime
designate Loken who neutralized all remaining Aesir and Vanir
affecting termination of conflict. Prime designate Loken then
initiated stasis of several seed races including Earthen, Giants and
Vrykul at designated holding facilities.
The Tribunal of Ages
Vrykul south of Northrend did not take part in the War of the Ancients, largely being concentrated in Tirisfal, where they followed Tyr and guard his tomb to this day. (Chronicles I)