@gantoine, I use hidden pages too but you don’t need a plugin for this (not saying you can’t use a plugin). WordPress has a nice exclude functionality so whenever you display the pages menu you can specify which pages you want to exclude from the menu (keep them hidden). When you add the “Pages” from the widgets menu you will see wordpress lets you exclude the pages that you don’t want to appear in the menu.
There are a few other plugins that does this exclusion too (e.g WP Page Exclude).
With that said, I read the description of the “WP Hide Post” plugin and it looks like it just doesn’t exclude the post or page it can put another layer of protection too. Please note if wordpress can’t access a post because this plugin is hiding it then the WP eMember won’t be able to access it either.