Found the answer via Nova's developer (the answer is no unfortunately):
Google Now integration, in the exact same way that Google does so, is not possible. This includes the swipe to the left for Google Now and the "Ok, Google" hotword. The Google Experience Launcher (GEL) is not a stand alone component, but actually a bundle of Google Search, Google Now, and GEL. With current APIs, it's not possible for Nova to access Google Now in the exact same way that the GEL does. However I am looking into ways to achieve similar functionality. Quick access to Google Now is already possible by swiping up from the home button (on devices with navigation bars), or by assigning a Nova Gesture to launch Google Now. Some users have suggested placing a full screen Google Now widget on the left most page. I'll be investigating further enhancements in this area, but it's important to note that the exact Google experience is not possible for non-Google apps.
Hope this might help someone else.