The hue bridge does not automatically expose all devices connected to it to HomeKit. So you will want to look into that first. For example, if you add a tradfri bulb to the Phillips hue bridge, it works fine with Alexa or with smartthings, but it won’t be visible to HomeKit. (By the way, the same thing is true if you add a Phillips hue bulb to the tradfri Gateway. Apple has very strict security requirements for bridges.)
https://www.reddit.com/r/HomeKit/comments/7om1w8/ikea_trådfri_on_homekit_via_hue/
@anon36505037 May have some additional thoughts.