Joel Greenberg, a onetime local official in Florida, is accused of an array of crimes, including bribery, stalking and corruption.
The congressman defended himself in his first major public appearance since a Justice Department inquiry came to light last week.
The associate could cooperate with prosecutors, giving them information about Mr. Gaetz’s relationships that investigators are examining for possible sex trafficking violations.
The Justice Department is said to be investigating the congressman’s encounters with women recruited online for sex and whether he had sex with a 17-year-old girl.
The congressman and a former official in Florida sent money to the women using cash apps, receipts showed.