It depends on what information you want to share about that customer. You can share transaction and experience data with an affiliated insurance agency without providing an opt-out. The fact that a customer is a customer is experiential. The OCC has said that other identification-orient information, such as address and phone number, are also considered transaction or experience data and so not subject to opt-out under FCRA.
I do believe that you have to include in your privacy notice a statment that you share information with your affiliates as permitted by law. If you said in your privacy notice that you do not share any data with your affiliates, I would recommend sending a revised notice before sharing.