I misunderstood. I guess you are just missing the vignetting option in Aperture's raw converter? I thought you were shooting raw.
You could edit in Capture and open the image in Aperture as a TIF but I don't think that is what you want to do. It's hard to visualize two apps editing the same raw data (or maybe I misunderstand again ).
I should add. to be very clear on my example above, that the "out of camera image" I posted above has "High" vignette adjustments (my standard setting now) cooked into the out of camera JPG embedded in the raw file.
If I turn off the vignette control the corner darkening is more obvious and darker. I assume it would have been equally dark if I had shot it with the vignette control off. But that gets into the fuzzy area of what is "put of camera" and etc., I guess...
A JPG shooter would see what I posted above, and think that is the "the natural lens output". A raw shooter using something else without a vignette control would see something different and much worse.