Venona data collection stopped in 1945 (although analysis did not), and McCarthy was not in Washington until 1947, so no, Venona was not detecting Soviet spies during the McCarthy era.
Also, these cables sent from Soviet diplomats contained many names one would expect on diplomatic cables, including FDR, who no one serious has ever accused of espionage. This includes people embassy and consular officials met with. Subsequently, everyone mentioned in the cables some have said are spies, with not much evidence of this. FDR was mentioned, is he a spy too?