Elgato Stream Deck does not require Elgato Gaming capture hardware or software to function. It is a stand alone customizable keyboard.
If you want, you can use Stream Deck to accentuate your Elgato Game Capture HD software experience.
However, you can also use Stream Deck exclusively with OBS, or with services like Twitch.tv, Twitter and TipeeeStream.
You can also use Stream Deck as an Application and File launcher, to use Hotkeys, to easily launch Websites, and to control Multimedia.