I haven't been able to find a definitive answer though I'm pretty sure the answer is no.
Can there be two of the same unit in the game. Not a named character or God, but a troop unit.
If there are no duplicates of anything allowed then it would seem that a gaming group only need one copy and so long as someone owns an expansion, everyone would have access to the pieces in it.
You could, though as many have pointed out the game is meant to be played as no copies of units.