OK, this is the email I received from Nik Software today after contacting their customer support late last week.
Thank you very much for your e-mail.
We´ve installed the latest versions of all our NiKs in Aperture 3 and had no problems installing and running all of them, but...
all Nik Plugins are currently not compatible with 64-bit mode of Aperture 3. We are working on a solution concerning this issue, but we have no time line yet for release.
There is a solution to work with our products on Aperture 3. Starting one of our products in Aperture 3 gives you a message box to continue in 32-bit mode. Just click on continue and work in 32-bit mode.
If you want to launch Aperture 3 in 32-bit mode in general, please go to programs - aperture 3 - context menu - information and mark 32-bit starting option.
If you have any further questions, please do not hesitate to contact us.
Kind regards from Hamburg
Nik Support Team