No, it is not true. Many paintings by Rembrandt have been claimed as portraits of Jews, but the Portuguese Jews of Holland rarely had portraits painted. Only one portrait still stands securely. Many other paintings have been claimed as showing a particular interest in Jews, but they can equally be regarded as reflecting Calvinist interest in the stories of the Hebrew Bible. Other paintings formerly listed as showing Rembrandt's Jewish interests have been shown to be by his pupils.
Although many Dutch intellectuals were deeply interested in dialogue with Jewish scholars, Rembrandt was no great thinker. If anything, he seems remarkably uninterested in the Jews, for a man who lived and worked in the Jewish area of Amsterdam and who certainly had some identifiable Jewish friends.
Ruisdael's paintings of the Sephardic cemetery, de Witte's paintings of the synagogue, these can be seen as having a specific interest in Judaism, for different reasons. The melancholic view of the cemetery might be read as a reference to the remnants of the "Old Covenant" or the once glorious Jewish community of Iberia, whereas the synagogue, founded after Rembrandt's death, is one subject among many other paintings of sacred space by de Witte.
What is interesting is why Jewish interests, and even Jewishness itself, should have been attached to Rembrandt. Both Jews and anti-semites long took the connection for granted. This caused a severe problem for the Nazis during the 1940s, when they wanted to claim him as a great Aryan. The Nazi response was the subject of an exhibition at the Resistance Museum in Amsterdam, during 2006.