Is owned Gemini Air able to be used for Directv service

Hey @gmnineagan. Ongoing functionality and support are not guaranteed for unreturned leased equipment, and paying the $120 non-return fee does not officially transfer ownership - it is a penalty for failing to return the leased hardware. 

For the best experience and to stay compliant with your agreement, return the device when it is no longer needed. More details here: DIRECTV Equipment Lease Agreement - Legal Policy Center Rizza, DIRECTV Community Tea

If you got the Gemini Air from DirecTV (lease) with 24 month service agreement, if you cancel it then it is required to be returned to DirecTV as you don't own it. Yes you would be charged a non-return fee (what I think you meant by "$120 for non-payment"). Device deactivated means you cannot use it with your service anymore.

That was the main difference between DirecTV via Internet and DIRECTV STREAM. They provide you equipment with you agreeing to stay with them for at least 24 months and that you return equipment upon canceling it. With STREAM, it is a Bring Your Own Device (BYOD) model, meaning you use whatever box you buy yourself (Roku, Firestick, or a Gemini through an authorized retailer for the owned option).

But no, you cannot deactivate a box you don't own and use it for free. They have it setup to prevent exactly that.