I've seen Waters in concert several times, along with Gilmour, and the Gilmour-led Floyd. Roger's 'The Wall' in 2012 was probably the best show I've ever seen, followed by the 2017 tour. I never heard him say anything antisemitic, though I do hear him criticizing the actions of the Israeli government. I read an extensive interview with him a couple years ago, and he wasn't totally coherent when it comes to Israel vs Palestine, but again, I didn't read anything antisemitic. Maybe someone can clarify if I missed it.
No, he's never worn a Nazi costume onstage. As part of The Wall, he wears a fascist costume that resembles a Nazi uniform in order to depict the evils of fascism. That's part of what The Wall is all about. During the 2017 tour, he depicted various religious and monetary symbols all being dropped from a plane like bombs. It was a metaphor, you see. Apparently there were objections to the Star of David being shown in quick succession with the Dollar symbol, though the Cross and other symbols were included in the depiction as well. So he simply changed the order of the symbols and that was that. If you watch The Wall movie during the song Goodbye Blue Skies, you'll see such depictions are nothing new.
The rift with Gilmour is decades-old, tracing back to his 80s-era lawsuit claiming that Pink Floyd was creatively spent without him. They slag each other in the press at times, but Gilmour is more than happy to make money performing tunes that Roger wrote. They both still release solo albums, but none are as good as when they were working together. A year or so ago, Gilmour's wife Polly Samson criticized Waters as being antisemitic, and Gilmour made a statement agreeing. In preparation for his 2024 tour, Gilmour announced that he might skip the 70s-era Floyd tunes written by Waters, but Polly convinced him otherwise. Again, he's willing to play them when money is on the line.