Giancarlo Prete and Carla Romanelli were both among the Italian guest stars in RETURN OF THE SAINT too, and it certainly sounds as if they supplied their own voices.
Romanelli too spoke English very well - even if she had an Italian accent. She also appeared (speaking in her own voice) in the infamous Pia Zadora film THE LONELY LADY (1983), which was filmed in Rome. She was also doing some acting in France around this time and her career seemed to be doing well, so I wonder why she just dropped out of sight...
Those wanting to see more Euro actors guest star in American TV shows should pick up some episodes of I SPY on DVD. Several episodes in the second and third season were filmed in Italy and features guest roles from people like Gordon Mitchell, Barbara Steele, Massimo Serato, Raffaella Carrà , Caterina Boratto, Fausto Tozzi, Gabriele Ferzetti, Leopoldo Trieste, Paul Muller, Marino Masé, Samson Burke and Delia Boccardo.
Also, the third season of IT TAKES A THIEF filmed several episodes in Italy. Euro guest stars include: Delia Boccardo, Adolfo Celi, Edmund Purdom, Nicoletta Machiavelli, Venantino Venantini, Françoise Prévost, Paola Pitagora, Massimo Serato, Jacques Herlin, John Stacy, Bill Vanders, Ann Smyrner and Marino Masé. Sadly, I don't think this series has been released on DVD...