What do the chmod do there? Removing files count as writes to the directory at least in Linux, so chmodding the dummy file wouldn't do much I'm thinking.
Yes sure, but I question if these permissions would do anything to prevent that. It would reject an open() call on the file, but these are expected to be directories so that would never happen, and it doesn't stop an unlink()
I would also set the ‘user immutable’ flag. If you want even better, set the ‘system immutable’ flag (see ‘man chflags’)