Three issues with GameObjects marked as NotEditable:

1) In a hierarchy of NotEditable objects, you can drag and drop an editable object inside the hierarchy. You can then make a NotEditable object a child of that object. Images 1.2 (drag), 1.1 (drop), 1.3 (re-parent).

2) In a hierarchy of NotEditable objects, you can drag an object outside of the hierarchy, therefore modifying the "parent" property of the transform. Images 2.1 (drag), 2.2 (drop)