Not exactly. So to clarify -
If your goal is to make the ecobee sensors available to Home Assistant: I believe you would have to unpair the ecobee (the unit, not just the sensors) off HomeKit, leaving the ecobee in a “hey I’m open for pairing” state, and then, chances are, the HomeKit Controller integration of Home Assistant will discover/grab/integrate the ecobee into HA.
So in the end the entire ecobee, the thermostats, the sensors, everything, would be available from your Home Assistant, via HomeKit (the protocol) and via the HomeKit Controller, (and thus not available to your HomeKit).
Does this make sense? Or did I misunderstand something?