Activating Restricted Games

Usually you can, depends on the game.

Read the thing about SteamDB If it's a Steamgift, most of them should activate.

Yes its possible, depends if the key is for example ROW or WW or if its a Steamgift. But games like DeadRising 2 for example are locked in certain countrys.

I remember The First Templar wasn't available on my region yet I was able to redeem a key of the game.

If you won it here and it's region locked, then that is against the policy of giving away games. Now, if it activates fine, then nothing is wrong. But if it doesnt, then that person is entitled to give you a RoW version.