Applications that operate on the basis of a libraries paradigm hide files in such a way that other applications cannot see them at all, no matter what.
A prime example is iPhoto. You have to export the files out of iPhoto libraries before Bridge can see them. I know this for a fact. While I have no such hands-on experience with Aperture, my understanding is that Aperture libraries behave the same way.
So, short of exporting your files out of the Aperture library, you wont be able to access them through Bridge.
If anyone else thinks I'm wrong, please correct me ASAP.
I have heard this about iPhoto. Never used it but apparently it creates packets of images that are hidden. Then when you try to open the image into PS by clicking on the thumbnail all you get is the thumbnail.