Fire Druid

[Wyrm]

Yes. An item generated in the gambling screen is considered "dropped" for the game's purposes, and thus cannot drop again.

Whether an item is rare/unique/set/magical is no longer determined when the gamble screen loads, but rather after you buy it. This was done to prevent people from using gambling sniffers to see what they would be getting beforehand. And unless you mean the same item seed #, then multiple uniques of the same type can drop in one game since Blizzard has long since removed the whole uniqueness to uniques.