Personally, I choose to add non-OS X fonts into my local fonts directory. It is located at /Users/you/Library/Fonts. This location is among the font search paths used by the operating system, and fonts added here, will also become available to applications, including Pages.
This has the advantage of not cluttering up the System font installation areas. It is not clear to me if major, or minor OS X updates will remove non-original System fonts as part of the installation process — as I have always used the local font directory.
Many new users to Pages also do not realize that the operating system also installs additional iWork fonts in an undocumented location. Until one adds a new font collection (call it iWork) in Font Book, and navigate to this folder location and include the fonts — they will be unavailable. See the Font Book Help topic, “Create font collections or libraries." Right-click on your new iWork collection in Font Book, and at the bottom of the contextual menu, choose Add Fonts…, and navigate to the following location. Single-click the iWork folder to commence adding its fonts.
/Library/Application Support/Apple/Fonts/iWork