A partir da descrição da propriedade de estilo oculto na API do OpenXml: link
This element specifies whether this style shall be hidden from any and all user interfaces when this document is loaded by an application. If this element is set, then this style can be used to format content (i.e. any content which references this style shall have its properties as normal), but the style shall be hidden from all user interface associated with that application. [Note: This setting is typically used to hide styles which are being used internally by an application which should not be used as formatting in a typical case. end note]
If this element is omitted, then the style shall not be required to be hidden from the user interface.
A partir dos sons desta informação, a minha aposta é que é uma daquelas propriedades orientadas para o desenvolvedor que não têm equivalente na interface do usuário e podem ser configuradas somente por meio de código.