No, Satori does not guarantee that the SVG will 100% match the browser-rendered HTML output. That's because Satori implements its own layout engine based on the SVG 1.1 spec. However, Satori generated result (SVG) is stable on all browsers.
This was the use case I had in mind. My company generates exports that are either PDF or PNG/JPEG images from the DOM using Puppeteer. We really wanted to support SVG but every option we explored had pretty significant rendering issues, meaning an entire rewrite in SVG would have been required.