Apple tends to be slow supporting new cameras, even top pro cameras like the Nikon D800 and the D4. They are not yet supported:
Alternatives while we wait for Apple to add Nikon D4 and D800 support include:
• Adobe's RAW converter now or very soon will convert the Nikon NEF files into DNG files Aperture can use.
• Nikon NX2 usually does the best job of converting NEFs (but without Aperture's elegant workflow).
Nikon keeps each camera's RAW conversion algorithms proprietary, so firms like Apple and Adobe have to sort of reverse-engineer for each new camera.
When Apple finishes the work needed to support the new Nikons they will issue a Software Update.
Horepower is also an issue because the D800 files will be huge when shooting at the full 36 MP RAW setting. For sure you want to upgrade to 8 GB RAM, and use a Referenced-Masters workflow with Masters on external drives (or add a large hard drive in place of the MBP optical drive).
just tested with some D800 Nefs ... they doesn't open in Aperture ... so in the beginning you would have to convert them first with capture nx and then import into Aperture ... shouldn't take them too long to update Aperture ... keep in mind that the d800 isn't officially sold yet