Can Unique maps drop, GGG?

The only Unique map we know of is offered as a reward in the HC Race, which suggests to me it's only available as a reward. But there's no way to know for sure, other than to ask!

So, should I Chance every single map I find in the hope for a unique, or is that currently pointless?

I'm pretty sure the only unique map in the game right now is the Vaults of Atziri, which should be able to drop. It's a Vaal Pyramid map, so don't waste orbs on anything else.