Every Pro bracket has an OBS view at /b/your-bracket-slug/obs. It renders only the bracket tree on a fully transparent background, with no header, buttons or voting controls, so it composites cleanly over your scene.
In OBS, add a Browser source, paste that URL, and set the width and height to match your canvas (for example 1920 by 1080). Because the page background is transparent, you do not need a chroma key. The view updates live as votes come in. Open the bracket page while signed in as the owner and use the OBS view button to get the exact link.
The OBS overlay is a Pro feature. On a free bracket the link shows a short notice instead of the bracket, with an upgrade button for the owner.