When performing the actual join process to the domain, you can use any AD server. It is a one time setup process. However, when you create your Authentication Source to use Active DIrectory, you can then use primary and backup (or multiple backup) servers to reflect your desire to use multiple domain controllers.
OR, you can just specify your domain name and allow AD DNS source the best DC for you.
You can backup servers and separate tabs will be made for the Authentication source to use multiple servers.
