I don't know about entering a swim surface/region through a ladder but I know that exiting one through a ladder works. I had done that in Ahra Pahts at some point to create an exit to the water canals, and it worked. That was over two years ago, so I'm not sure what version of PyPRP it was.
About Anhonay: I think it is actually a custom animation rather than a regular ladder: 'Ahnonay_District_FemaleSwimDockExit.prp'