Description of problem:
When provisioning a discovered host, "Host Group" is not marked as a required field even though that machine will fail to register back to Satellite without it (since host group contains the activation key).

If the system does not register back to Satellite you can't manage it. Therefore either the Host Group should be required (and the Host Group should have to have an Activation Key) or there needs to be some other way to add an Activation Key to the Host (and it needs to be required, or some combination of the above needs to be required).