Richard the Lionheart was notoriously enthusiastic about murdering Jews nearly wherever he found them, and massacred them and destroyed their quarter when he took Jerusalem. After Saladin retook the city he reestablished the Jewish quarter.
Is there any evidence Jews may have helped Saladin retake Jerusalem.
Not really. The Jewish community of Palestine was mostly killed by the Crusaders, particularly in Jerusalem, and those who were left were generally ransomed. There weren't Jews around to help. There were others in other Muslim areas, but there doesn't seem to have been an organized effort to assist Saladin's reconquest.
Also, the concept of "Jewish warriors" isn't really a "thing" in Medieval Jewish history. Jews were generally a class unto themselves in social hierarchy, and thus would not have been part of a professional military. There were some Jews who fought in the First Crusade against the Crusaders defending cities, particularly in Haifa. But they seem to have been locals who joined the defense of their homes alongside the Muslim armies, but were never actual "warriors" in any sense.
So there's no evidence that there were any. Jews did fight crusaders during the first crusade, but there were no "Jewish warriors" as such during this period, or really any period after antiquity until emancipation (with the possible exception of the Himyarites (sp?) in the Arabian Peninsula).
Source: Gil, Moshe. A History of Palestine, 634-1099. Cambridge; New York: Cambridge University Press, 1992.
Incidentally, Richard was not a particularly anti-Jewish ruler--see my answer here. While he wasn't exactly friendly, and the condition of Jews in England deteriorated during his reign, it's not clear that he's the reason. And your chronology is a bit messed up--the huge massacres of Jews were during the first Crusade primarily, which is when Jerusalem first fell to the Chrusaders. Richard fought in the 3rd crusade.
There is no record of Saladin having any Jewish soldiers in his army. From what I have learned, it was made up mostly of Syrians, Egyptians, and Turks.
It wasn't so much that he teamed up with Jews to defeat the Crusaders, or even an "enemy of my enemy" situation. When Saladin retook Jerusalem he did not seek revenge with murder and looting like the Crusaders had done previously. He was just as kind to Christians as he was to the Jews, allowing them the same freedom to live there and allowed pilgrims into the city afterwards.