I figured out the answer to your question. You can transfer multiple photos from Aperture into an Event. And it is pretty slick. And you do it through the Photo Browser. I have not tested it with video in Aperture, because I do not keep video in Aperture. But it probably works, but in any event it works great for photos.
There is a trick to this, that I have not seen documented anywhere, but sometimes having a knowledge of how iMovie works comes in handy.
To do this there are three key components.
1) In the FCPX Photo Browser, you can select not only individual photos - you can select entire projects by going to the Project view and dragging in the whole project. In the Project view of the photo browser, you will see your projects as a box that you can skim to see the contents. You can drag this whole box into FCPX all at once.
2) But the entire Aperture project level may not be what you want. What you might really want to import is an Aperture Album, Smartalbum, or Faces or Places selection. You can do this also, but not by dragging in the icon. In this case, you click on the Album (for example) in the Photo Browser. There will be a check mark next to it, and the album will open. You can select one photo. You can select multiple photos in the album by command clicking. And you can select the entire album by clicking one photo (so the photo browser has the focus) and then hitting Command-A to select All. Now you can drag all that you have selected into your FCPX event.
3) This is the key part. So you create a new Event in FCPX. It will come up with a blank event, and it will invite you to "Import Media". However, you cannot drag stuff there from the Photo Browser. However, you CAN drag to the Event Name over in the Event Library List. You drag either your Project or your selected photos from an Album, SmartAlbum, Faces or Places and drop it on the Event Name in the Event Library. Your cursor should show the green + sign to indicate that you are over a valid dropzone. Done.
4) If you prefer to use Aperture itself rather than the Photo Browser, this also works. You select your Project, Album, etc. Then Command click or Command-A to select the contents of the Album you want. Then drag to FCPX and drop on the Event name.