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Most free games require you to go through sign-up/Like-this-and-that hoops.

If you start nitpicking what hoops are and aren't permissible, it'll get convoluted.
So no, I'm with Freekill, at least while this game is available for 'free', it shouldn't be able to be posted.

On the flip side, it's a pretty special scenario, since while you aren't spending any currency of any sort on the game, you are investing time to earn it, which would be more akin to using an earned voucher than treating it as a giveaway.

So you could make a case for it; in the end, it's really up to the SteamGifts devs.