It's not rash judgement. Your Uncle married a divorced woman. Why, or how, is it known that she was a divorced woman? What is the level of Catholic knowledge or commitment in a man who does such a thing knowingly?
Rash judgement would be saying that your Uncle is on the way to Hell. That would be rash.
Advising him to seek out a Traditional Catholic Priest for advice on his current marriage would be a prudent thing to do.
1. While my uncle did marry a divorced woman, that doesn't mean he wasn't validly married. Could be any number of reasons, including: Pauline/Petrine privilege, annulment of her previous marriage, or the previous spouse is now deceased. Terminology can be muddied in the modern world. Yes, sometimes people continue to identify as divorced even though they are not, or a widow, by Catholic thinking.
2. Many circumstances can affect a marriage. Especially if prior attempted marriages are involved, things can be complicated. Then there are issues of justice for any children. I do know what was going on with my uncle. The busybody who approached me about my uncle knew who I am and what my background is. The person frankly should have trusted that my uncle's situation was already checked out. Should I have had to explain my uncle's marriage to everyone who asks? There can be circumstances of a marriage case that are "private" or inappropriate to discuss, perhaps because they could reveal or imply sins of another, and so would be an injustice.
3. I'm saddened to see the people arguing about this. My post referred to a busybody who didn't have all the facts. Arguing against me has been a resistance Mass coordinator who went to SSPX seminary but (if I recall correctly) never studied moral or pastoral theology there. The one who accused me of being "Bergoglian" also went to SSPX seminary but (if I recall correctly) also never studied moral or pastoral theology there. I don't know you, but still that's three people doing pretty much what I was identifying with the busybody. None of you know the circumstances but still seek to provide "advice". This probably falls short of"rash judgment" due to lack of firm judgment (perhaps it's "rash suspicion"?). Nevertheless, this sort of behaviour is something I associate with the old ladies of a parish.
4. More broadly, this thread is an example of a trend that gives me pause about the resistance segment of tradition. I agreed the way annulments are handled in the US isn't right. But here I get "downvotes" for expressing some traditional pastoral theology, and some leading lights of this forum appear to argue against that theology, based on an ideal of what society should be but currently isn't, or because it sounds liberal. This is an example of why I suspect even when/if Rome did return to tradition, it may not be accepted by many traditionalists, who sometimes have peculiar notions of "tradition".