The hue bride contains its own http server and therefore the API can be accessed locally. It is not homeKit, it is local over ethernet, but it relys on the api, which is local. It uses the hue-bride-specific API which is well documented, you can get access here:
I had experience with the home bridge Hue plugin (GitHub - ebaauw/homebridge-hue: Homebridge plugin for Philips Hue) and indeed it communicates with their API locally as well. I found that this plugin was more feature rich than the official homey hue app, so that means that there would probably be room for an improved community Hue bridge app.
One more question: can the Hue bridge be also connected via Matter ? The Hue bridge is itself a Matter bridge and Homey is a Matter controller, so this could work? Just trying to understand the ecosystem.
Before creating one, ask Athom if they will actually allow it in the app store. Officially the guideline is that there should be only one app per brand and that developers are encouraged to work together by issuing PR’s against the app that already exists, but that guideline is immediately negated by Athom pretty much making all their own apps closed source.