I recently purchased an Xbox One and haven't been able to redeem the backwards compatible Xbox 360 (Dragon Age II) and original Xbox games (Mercenaries: Playground of Destruction). Participating Xbox One games have games have been added to my account so far, but the legacy games display a price.
To my knowledge all games given for the Gold subscribers run on Xbox One and don't require legacy hardware to redeem -- Xbox Live for the original Xbox was discontinued in 2010.