Traffic between AP and ZD should not be much. I don't have stats for what you are looking at. Ruckus Folks would have for sure. My hunch is that you are tunnelling your WLAN traffic from AP to ZD that is why you are seeing high usage b/w ZD & AP.
See here on what i meant - http://prntscr.com/487rnk
Path is ZD GUI -- configue TAB -- WLAN -- Edit - Advanced options.
Hope this helps.