To my knowledge, no one has come up with an effective treatment other than high quality water, uv sterilization and a dark burrow. There is some evidence that the pathogen(s) are contagious, so I would avoid placing a healthy stomatopod in the same water system as an infected one. Again, if you don't see a rust-colored spot on the carapace (which I though I saw in one photo), don't worry. The disease is very slow developing. It was probably just a reflection.
The only sure way to sex O.s. is by the genetalia. The male has a pair of peneis hanging down off the inslde of the last pair of walking legs. In large animals, males are often more green while females are olive, but that is not absolute.
Roy