The easiest way to be able to search your files would be to import the files as "Referenced" files. Aperture will place a preview in the database but the actual file will remain in the location you have it stored. So for example, if you have all of your NEFs/JPGS on an external drive in a folder directory, importing as referenced files will leave them in your original location. There is no need to import them into the database unless you want Aperture to manage all of your files.

Joe