Will I be able to use my Ring doorbell with Connect Fibre

You will be able to use your Ring Doorbell without any issues

Ring doorbells connect directly to Ring's servers when they are setup - this happens when you scan the QR code or enter the MAC ID of the device into your app. This allows the doorbells to be setup quickly without e.g. having to forward any ports.

You can view your doorbell feed from anywhere in the world - because you are actually watching the stream via Ring's servers i.e. the stream isn't being served by your doorbell.