I'm saying the pitcher never has a spot in the batting order. They would be treated as a special case. So Ohtani would be the DH who just happens to be filling a dual role and also be pitching. If someone else came in to pitch, it would have no impact on anything else. Ohtani would still be the DH and would no longer be pitching. Once he left as a pitcher though, he couldn't come back and pitch again in the same game.
I don't know if it's a good idea or not, but it would make some degree of sense.