This is maddening.
It works sometimes, not others.
When I turn the camera on, EOS Utility opens automatically AND Aperture tries to import any images on the memory card.
If I quit EOS utility and activate tethering, Aperture tells me there is no camera connected.
If I use EOS to tether (or remote capture) I can 'register' Aperture as an application to receive RAW images, but... it creates a new Aperture project for EVERY SINGLE image it imports.
I cannot for the life of me get tethering working again completely through Aperture... although previously I had it working for about 6 photos.