I would say no… unless you want to image the partition and go at it with a file carver (which wouldn’t care what the fs is as long as it wasn’t fragmented i think) which would be quite ambitious… I don’t know if there are any file recovery tools for BFS
dunno
I don’t see any problem… how did you install? just dd it to the partition if so the old install should have been obliterated. If you mounted the image and copied it out from a separate installation of haiku/beos/zeta then I imagine there could be issues if you didn’t do it carefully making sure all the old files were gone