I have half a dozen Hue dimmable bulbs. I do not use a Hue (brand) hub. But I did get a more current Amazon Echo which supports Hue bulbs.
I suspect that the Hue bulbs are “proprietary” and you must have a hub in order to use them, unlike a lot of current bulbs which are open Wi-Fi or Zigbee? If so, they will be out soon. I’m headed as much as possible to an open system.
If so, which is “better” for dimmable bulbs? Zigbee? Or Wi-Fi?
Hue communicates over Zigbee and for that it needs a coordinator, currently that’s your Echo. I can’t tell if the echo is able to expose the bulbs to openHAB, if not you need to switch to another coordinator.
You can use a zigbee stick, generic zigbee-bridge or the Hue-bridge for this, the latter can be used locally without cloud.
Personally I like the HUE lights and these integrate well over the bridge, but they work just as well using an alternative like zigbee2mqtt or the openHAB zigbee binding.
I use them mainly for accent or mood-lighting, main lights are zwave operated dimmers with normal warm-white dimmable led-bulbs.
That would indeed work for me (for now).
I have WiFi devices (2 LED lights) that are controlled BOTH by Echo and OH which is maybe a slight plus (and probably a recipie for disaster. ). I know if I reteach the Hue Bulbs to OH, then Alexa would have to control via OH. Which is FINE with me as well.