Hi Slevin55,
I can confirm, that it is possible to access to any picture file by either pressing the replace radio button as it is written by thenez or via menu 'insert' and 'choose' as written by Bwh888 - but I can't open the Photo-Library even if I made all files visible before. It's obviously not possible to open the library as a package.
Finaly I don't know any way to access directly to an Aperture-Library within Pages 5.0. But I solved the problem this way:
I started iPhoto 9.5.1 while pressing ALT. Then I've choosen "Create New..." (in German "Neue erstellen..."). Check in finder by "Get info", that the new library is of kind "Photo Library", Version "iPhoto-Mediathek 9.5.1" (perhaps in English OS "iPhoto-Library 9.5.1"), neither kind "iPhoto Library" nor "Aperture Library".
Then I closed iPhoto 9.5.1 and opend this newly created library in Aperture 3.5.1. It was empty, of course. Now I took my old Aperture-Library (about 25 GB) and imported it into the empty new Photo Library by drag and drop. Ok, it took hours to finish, but then I had all my stuff in a Photo Library, that can be opened in the mediabrowser of every app of iWork like Pages 5.0.1 without any problems. The library itself increased a bit (100-200 MB), but I think it's ok. The new Photo Library can be opend in Aperture and iPhoto as well.
So try to go the same way. Hope, it works for you too.