"Fiyero saw what the Wizard did to Dr. Dillamond and still joined his ranks!" Now, see- that's where you're quite possibly flat out wrong. You're assuming Glinda told him the entire, full truth about the Animal genocide being orchestrated by the Wizard in the first place. As if homegirl hasn't manipulated her ass off in the past to get what she wants, or get rid of what she doesn't want. She knows how to clock social ques and manipulate the truth to fit her desire- telling Boq to ask out Nessa, giving Elphaba the hat, sensing the romance between Fiyeraba at the train, belittling Elphaba in DG in hopes for her to stay, banishing the Wizard when he's at his lowest (i.e finding out his daughter is dead). She may not be book smart ("form over content," "instead of always harping on the past," "they were popular," etc etc), but she sure as hell knows how all the social cogs work.
And considering that movie!Fiyero seems to be much more Animal-ally inclined than his musical counterpart, I would be... honestly, I'd be shocked if she told him everything. Because although Fiyero would still stay so he can make sure nobody kills Elphaba, I doubt he'd even try to make peace with Glinda if he knew she, quite frankly, didn't give a fuck about the Animals. And I think Glinda would know that, and would deliberately leave that out when she tells him how everything happened. I won't ever deny that Glinda cares for Elphaba- but the thing that sets her and Fiyero apart is caring for the Animals. Which is also one of the reasons why in the end, it's Fiyero and Elphaba escaping together and not the three of them.
Also, please for the love of God, remember that nobody at Shiz knew the Wizard was capturing the Animals. The Wizard didn't want people to know he was behind the Animal propaganda and capturing. Otherwise Elphaba would have never gone to him in the first place- plus the fact that the uniforms for Fiyero's squadron and the squadron capturing Animals were entirely different. All in all, it is incredibly likely he just... doesn't know. He's, presumably, not in charge of the Animals, and again, all his information comes from Glinda. Known manipulator Glinda. Doesn't care for the Animals Glinda. Stuck in a bubble of privilege Glinda. THAT Glinda.
Now, I'm not saying its impossible that he knew. Maybe he did. Maybe he actively captured some. But the only line we get of him even knowing about the Animals in the musical is, "there's a goat on the lamb." When, mind you, he was actively pretending to hate Elphaba until he got rid of his guards and held the Wizard at gun point so he couldn't call them back. He didn't exactly have time to ponder Dr. Dillamond's presence when he knew that if he didn't get to Elphaba first, it would get ugly. So... could it change in the movie? Absolutely. But don't act as though anything is canon yet- people always yap about Fiyero and Fiyeraba being rushed as justification for Gelphie, but then turn around and get mad at Fiyerabas for "not holding Fiyero accountable" as if we're not lacking critical information. Can't hold him accountable if there's almost nothing canon to hold him accountable for.
