From wiki;
"The Huns first appeared in Europe in the 4th century. They show up north of the Black Sea around 370. The Huns crossed the Volga river and attacked the Alans, whom they subjugated."
If this was the case, why wouldn't they be playable?
EDIT: Also;
In 395 the Huns began their first large-scale attack on the Eastern Roman Empire.[15] Huns attacked in Thrace, overran Armenia, and pillaged Cappadocia. They entered parts of Syria, threatened Antioch, and swarmed through the province of Euphratesia.