I don't think they use Bing, but yes, Google, Marginalia, Yandex, Brave and others. I still fail to see how that's different to DuckDuckGo, who also run their own crawler. It's really weird that people are almost hating on DuckDuckGo for how they run their search engine, while applauding Kagi, for doing the same, but with a different business model.
You can buy access to the Google Search API, which is what I assume Kagi does. Building your product on being able to circumvent some Google restrictions seems like a bad business move, if you can buy the same service for a reasonable price.