For his son’s bar mitzvah in 2008, hedge-fund manager Murray Huberfeld chartered a JetBlue plane and invited hundreds to an oceanfront party in Palm Beach, Fla. An Orthodox pop star known as the “Jewish Elvis” entertained the guests, who Mr. Huberfeld says included investors in his fund.

Intimate ties and fundraising inside a close-knit world of observant Jewish businesspeople in New York, Florida and Israel are central to the $1.25 billion hedge-fund firm Mr. Huberfeld has helped lead, Platinum Partners. Now those ties are...