NI installer will put Kontakt AU plugin in Components folder. It will be sitting there, until you install any DAW, for example Logic. Then it will be scanned and recognised and you will be able to use it in Logic.
No problem. Logic always scans Components folder upon first run, after installation. Other DAWs which use both VST2/3 and AU (like Ableton Live) will also scan VST and VST3 folders.