The cave you are wondering about, "R" Cave, had two entrances. According to my info, one of them was lost in the flood/landslide. After seeing the devastation up there, I can believe it. The other entrance is still passable, though. (Are we not even allowed to mention cave names now? I thought the only restriction was on giving out locations. Just wondering.)
As far as Nash goes, I believe that the place where the waterfall drops into is the "pit." It has been many years since I've been there, but from what I remember, I went down and was unable to go past the pit bottom because of the high water flow. I didn't have a wetsuit at the time, but that is probably what you would need to access it safely, especially this time of the year.
Also, I am willing to bet that Ulla is totally sumped, and will be for quite a while. It is a nice cave- when I was there, we couldn't find our way to the waterfall dome at the end. It wasn't for lack of trying, either.