Trademarks are funny in that they are confined to certain markets. If you do not compete in a trademark owner's business, you can use the mark. You see this in the wild: the word Namco, for instance, is trademarked to a Japanese video game company and an American swimming pool company. The word Shazam can refer to a superhero owned by Warner Bros., an app owned by Apple, or a financial services company called Shazam Inc. with a separate trademark for all three. And there's some interesting trademark history behind the name "Apple" itself!

So yes, while the tetrominos being a Tetris Company trademark precludes their unlicensed use in video games, they can be used in other contexts -- a tetromino pattern on pyjamas or wallpaper, for instance.

However, I would be wary about attempting to use them in a board game, as I seem to recall at least one licensed Tetris board game in the wild. Consult an attorney before proceeding. :)