As far as I know it is not possible to scan photos from within Aperture. Pictures need to be scanned outside Aperture, then saved and imported.

But there is a time saving solution: scanning to Aperture using Image Capture (included free with OS X), if you don't mind to use that program for the job.

Start Image Capture, choose your scanner on the left side of the screen, and at the bottom, click “Show Details”. At the right side choose the appropriate settings. For “Scan To”: choose Aperture. That's the trick!

Instruct Image Capture to scan photos directly into Aperture

After scanning you will find your images in Aperture in a new project, probably called Untitled Project, followed by a counter number between parentheses. With each new scan, the images are stored in a new project. If you are not happy with images scattered over several projects. They can be dragged from one project to another manually, or they can be merged into one project in one quick step.

To merge projects, simply…

1. Select all the projects you want to merge
2. Choose the command File > Merge Projects…

All images will be stored in the most upper project selected, and the empty projects will be deleted!