Can Aperture open/view/edit a Photos library?
Here's what it says in an Apple Support article:

iPhoto — and Aperture, if you downloaded it — remains on your system in the Applications folder, and you can continue to use it. If you open iPhoto or Aperture after you upgrade to Photos, you’ll be asked if you want to open your library there or in Photos.
Any changes or edits you make in iPhoto or Aperture aren't reflected in Photos. And any changes or edits you make in Photos will not be reflected in iPhoto or Aperture.

It appears that you are able to open photos within both applications however edits will not be synced between Aperture and Photos.