You realise minato already established that he was possibly Madara and that he was controlling Kurama via genjutsu. Hence why minato used a contract seal on him and avoided eye contact the entire time, after minato removed his control. I highly doubt there was even a threat of genjutsu because controlling Kurama would've already been a difficult task to do, trying to genjutsu someone else simultaneously.. Yeah I don't think so.
Still find it astoning that people think Hokage's - the people who commanded uchiha, had intel on them, were stronger than them, and especially Minato who had intel on the real Madara, would fall prey to genjutsu U_U Even reckless Ay told Sasuke his eyes wouldn't work on him and was ashamed when he got caught by Madara's (due to distraction). Ohnoki knows not to look directly into Madara's eyes (he didn't get caught at all).
No Hokage, even Tsuande has ever been shown to be caught by an uchiha genjutsu, because it wouldn't even make sense since they should know the most about uchiha. Even Tsuande didn't get caught once, despite getting close to Madara several times. Both Hashirama and minato have fought the 2 most powerful uchiha, and neither had an issue with genjutsu.