Doesn't work for me. My Aperture Library (.aplibrary) 3.5 it's now my default iPhoto library and still doesn't work:
I figured this out: Instead of using media button on the toolbar, click "Insert" from the top menu and "Choose" on the very bottom. A finder window will open, in the left pane click photos. You will see a new page open with two panes. Top pane will have expandable links: Aperture, iPhoto and Photo Booth. Click on "Aperture" and it will expand to show you your full Aperture library. Choose the project and then choose the photo.
In the old version i was able to choose media and photos from my Aperture library directly, in this new and improved version you have to make a few extra clicks.
I figured this out: Instead of using media button on the toolbar, click "Insert" from the top menu and "Choose" on the very bottom
A great discovery! Indeed, the "Insert > Photos" will let you access all your photos, including the current Aperture library.
But what a mess - now we have two different ways the Media browser is working in iWork - from the Finder's sidebar you can add photos from Aperture and from iPhoto to your document, but from the media browser panel not. and unfortunately you can only add new photos this way - you cannot fill the predefined photo placeholder images. The links there will only open the Media Browser Panel, not the "All Photos" chooser. So I still found no way to replace placeholder images by Aperture images.