I have!
It was during a summer visit, while they were open til late for the evening parade at entrance.
On the way, I stopped by just to see if I could catch a glimpse, and I did! It was bounding across the enclosure, couldnt get a picture, but got a low quality video of it!
Much smaller than the wallabies, which this picture is.
I saw the bettong last year in one the koala yards. It emerged shortly before closing as the sun was beginning to set, quickly darting around the enclosure.