Ive done it, plenty of times. Which is one of the reasons steam shut down gifting games from russia (along with the whole currency drop thing). There were plenty of reputable russians out there, so you didnt have to deal with dodgy key sites, who would sell you the game for the russian price with a small mark up on their end. They are completely legit in the instances where games were not region locked which used to be the vast majority. Its how I got the latest civ game for 60% off for a pre-order. Russian prices are usually vastly lower than the USA pricing, i.e. GTA V is 30$ there, the latest COD was 15$ at one point
the only time its not legit is when you are required to use a vpn in order to activate your game since you are violating the TOS at that point. But to have a region non-locked game gifted to you is no way against the TOS. The reputable sellers wont sell you those games anyway since it impacts their business as well. Since you are getting the game gifted the chances of a bad key also go way down, its already in their inventory and most likely purchased directly from the store
As another reply said, go look at nuuvem, as long as a game isnt region locked to brazil (their country of origin) they have no problems selling you a game, which is usually at a vast discount because there are no issues with it, the key could from from the USA, UK, it doesnt matter, its all from the same pool at that point.