Try the following:

1. Open Aperture.
2. Open Aperture Preferences.
3. Click on the Preview tab.
4. In the "Share Previews with iLife and iWork" dropdown, select Always.

Your photos/Aperture-related media should appear in iMovie if you press Command+2 (or whatever hotkey you have that enables the "show/hide Photos browser".

To get Aperture to show up in the Event Library, quit and reopen Aperture. Be sure to let iMovie generate thumbnails from the Aperture library scan by clicking "Now".

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Alternatively, you can always go to the movie in Aperture, right-click it, and select "Edit with iMovie" directly.