The Aperture library is a library package and not an image file, so Spotlight will not show the library as an image but as "other". Since the unified library format has been introduced, iPhoto images will not be shown in Spotlight either.
The usual way to search for images managed by Aperture should be to use the elaborate search tools provided by Aperture - smart searches and smart albums or the Media Browser to access them from applications that can browse iPhoto and Aperture libraries, like Mail, Preview, iMovie, ...
If you want Spotlight to be able to the original image files of your Aperture images, convert your Aperture library into a referenced library (see: Aperture 3 User Manual: Working with Referenced Images). This way, the original image files will be stored in a folder outside the package and Spotlight or Find will see them. Only, if you decide to do that, remember that it it not save to manipulate the original image files in any other way than using Aperture to do this - don't accidentally delete them, move them, rename them, edit them. Referencing is meant as a method to be able to store the bulk of your images on external drives, not to give access to the original image files.
Also, Spotlight will never be able to show you your edited versions, since they do not exist as rendered image files until you export or share them. So Spotlight can only show the originals.
Regards
Léonie