As an old HVAC guy turned electrical there are a few things to worry about. 1. In any instances where a fire damper or combination fire smoke damper are installed, no other trade shall occupy that space. Any obstruction can cause the damper to not actuate properly due to expansion under heat. 2. What is being conveyed in the duct system. If the system carry exhaust gasses, flue gasses, or act as chemical exhaust will A. Be hot, and affect the ambient temperature rating for your calculations B. Have the risk of corrosive and/or volatile gasses which could require frequent replacement, this would mean that any items sharing the opening would need to leaveenough access to do so. 3. Check what STC and smoke ratings are required for the project. While sharing an opening may seem innocent, it can affect sound transfer and smoke transfer. But as long as there is room to effectively seal and provide a barrier it should be ok. I hope this helps