The validity of natural law

According to this, could a legal argument be made in the famous Roe v. Wade case in the US that even assuming that the Constitution did not treat the fetus as a person, or that a law against abortion violates the mother's freedom of action in a way that is unconstitutional, natural law still takes precedence in legal importance over the Constitution and therefore the act of abortion itself is legally prohibited.

First, the problem is that here you are once again entering the legal field. If the court had decided on this without arguments from the parties, it might have been similar.
Secondly, even in the meta-legal field there is a significant difference between the cases. In the case of the Nazis, we have a claim from every person there who understands for himself that this is an act that should not be done, even if the law requires him to do so. This is obvious to any reasonable person. Therefore, we expected him to resist and refuse to take part in the acts of the Nazi regime. This is why he can be punished without specific legal justification, because he is guilty. But on the issue of abortion, whatever your opinion (and my opinion), it is clear that a significant part of the public is truly and sincerely convinced that it is legitimate. Here it is difficult to say that the woman should have understood that this is an act that should not be done, when the majority of the reasonable public does not understand this. She is not guilty as long as the law does not prohibit it.
The line is of course thin, because it is possible for a person to do an act that is considered by those around him to be a serious moral offense, but he truly and sincerely thinks that it is permissible. I suppose that was the case in the early days of abortion. That's why I suppose that many would have likened it to the Nazis, because in their eyes it was self-evident and there was complete social agreement on it.
But in the Roe v. Wade case that took place in 1973, that was no longer the case. On the contrary, the Supreme Court had already ruled that such a law was unconstitutional. In other words, there was already broad social agreement on the legitimacy of this act.
You raised an interesting point, which is related to the post I'm writing now. We'll see what I do with it.

Regarding abortion,
Those who allow abortions can argue that even if natural law or morality forbids it, the right to life of the positive law of the state does not include fetuses.
Regarding the Nazis,
The rabbi's argument can be formulated as a court preparing and killing them unlawfully for the sake of fixing the state.