The article linked above has certain value and many good reasons not to duplicate the links of a page. However, in a hierarchy, depending on the presentation of these duplicates (for example, under the same link in different navigation menus), an argument can be taken into account. I present in evidence this article from the same group (Norman Nielsen Group) on polyhierarchies.
Since menus are rarely, if ever, open at the same time, the duplication of links that fall ambiguously into several categories does not seem to have the same cognitive burden as multiple multiples that are visible simultaneously. As stated in the article, if the site is deep or complex, polyhierarchies may not be a good idea, as they may spoil such orientation techniques as Ariane's thread. But for simple sites and those that do not rely on orientation, several navigation elements can sometimes be a useful tool.
A map or tree sorting exercise with your users can help you determine if it's a good idea, of course.