The idea is you create 1 virtual bulb/dimmer in HA . Then get alexa to see this bulb via emulated hue or Nabu Casa . Then you can trigger the bulb to a brightness level via alexa routines. Then depending on the brighness set triger HA to do something.
Nabu Casa will import most HA entities into Alexa or if you dont want to pay a monthy fee you can set it up yourself Amazon Alexa Smart Home Skill - Home Assistant
If you just want Alexa to speak the value of your HA controlled thermastat or any other entity value , I created this automation using the above technique.
Alexa Speak entity attributes. A Speech Engine.
I cannot see the advantage of creating fake Zigbee devices in HA , which will require real hardware to link them together , when you can create the same effect in software.
Am I missing something ?