The in-network or out-of-network distinction is always tied to who gets paid. And who gets paid is always the billing entity.
So - in your situation - who is the billing entity? Whose NPI Number is being submitted to the Insurance Carriers in Box 33a of the CMS 1500 form?
Since your provider joined something, I assume that the facility is the billing entity, with its own NPI Number and EIN. I assume that the facility bills, with its own NPI Number, the insurance carriers pay the facility, and the facility pays the provider for the work s/he does.
If your provider is the billing entity, and his NPI Number is placed into Box 33a of the CMS 1500 form, then the insurance carriers will be paying your provider according to whatever participating provider agreement is in effect.