I don't know--you could argue that Indy wants to study the Ark without opening it, analyzing its exterior and so forth but not risking the contents. In part to preserve them and in part because he knows full well how dangerous they are. Does that mean he wouldn't be tempted? Of course not. But I'm not sure he'd actually open it.

I do agree, however, that he and Marion survive purely because they don't look and so are spared the punishment such sacrilege demands.