No, you do not need a Google Account to enroll and manage a MC9300. You may benefit from creating an account for an Android Enterprise binding which you can then use to manage applications that you'd like to have installed from Managed Google Play on your devices. If however, you are not going to be installing any applications from Managed Play, and plan on installing any via APKs then you could avoid the need for an Android Enterprise binding. In that situation you can create an Enrollment rule set up to skip the binding step and to skip the creation of Managed service accounts on the device.