I've checked the behaviour on Windows and it's different in the file browser and the regular `Add file/folder` buttons:

* In the file browser, the `show hidden files` option has the expected effect (hidden files/folders will be shown or, well, hidden)
* The `Add file/folder` buttons seem to use the native dialogs for browsing and, as such, the behaviour in them does actually depend on the explorers settings regarding hidden files.