Teloch asked: New thoughts. If in the event that Ozai found out about the secret love between Zuko and Azula, how would he react? Would he care? Would he try to use it to better control his children? Would he try to NTR Azula at any time just to hurt Zuko? This question can also be applied to the whole Fire Foursome so I'll repost this question on that thread.
The other thought is, what if their roles were reversed? What if Azula was the untalented but gentle soul while Zuko became the twisted weapon of Ozai? Would Azula be able to save her brother?
Whether or not he would care would depend on how the Fire Nation viewed incest (I can't see Ozai having any moral problems with incest... or with literally anything). If they were one of these royal families that believed incestuous marriages would produce strong heirs and "keep the bloodline pure", or at the very least had a history of marrying relatives to each other either by tradition or to keep all the power to themselves, he would, at the very least, consider having Zuko and Azula marry each other. If their nation was violently against it, he'd either tell them to make sure no one ever found out about it, or full on try to separate them if he believed it was only a matter of time before everyone found out about it. If the nation was indifferent to it, he would plan neither to separate them nor to have them get married...
...But I can easily see him using their relationship as yet another "weapon" of his. He could try to use their love for each other to make them fight even harder to win and to make sure neither of them would ever turn against the Fire Nation (since that would mean putting the other at risk), and he'd definitively try to see if Azula could control Zuko and/or make him "stronger".
However, if he believed Zuko's influence and Azula's love for him was making her "weaker", he'd not only try to separate them, but if the Fire Nation did have a story of royal incest, I can see him at the very least considering marrying her (whether she agreed to it or not) to teach them both a lesson and to "correct" Azula's behavior (little does he know that would easily make him die of a sudden case of a sword plunged to his heart, another to his gut, and throat cut open).
I am very, very, very suspicious to talk since I'm biased as hell when it comes to these two, but I feel that regardless of what happened or who was the prodigy, Zuko and Azula would find a way to end up together... but not necessarily redeem themselves (though that is my preference). If they got together, their priority would be stay together, no matter what.