1) It is possible to set custom field required and not show it on general tab. In this case you can't create user in adm.console due unexisting field's requirement on general tab. Maybe, on custom field create/update, if field is required - set it automatically as shown on general tab to avoid described potencial problem.
2) Maybe "Field Prompt" on custom field creation must be required. If this field is empty, in adm.console field is displayed without label. Or maybe some hint is necessary besides "Field Prompt" to warn about such a behavior. Otherwise lazy administrator fills only required "Field Label", '"Heading" and thinks all is ok.