no, if using wordpress just make sure only tagged pages are linked to show on the front page.. or setup a static page which you choose which categories to show
Just publish a post and don't attach it to a category. You can make one or multiple internal links to get to post indexed or you just put a link to your sitemap in your footer.
With a sitemap Google knows all your published pages/posts/cpt's/categories/tags/etc (you can set this up) even if this post is not visible on your homepage or other pages. You can use Yoast, all in one SEO or a different WP plugin to set up your sitemap.