Interesting film. I have it on DVD. I’d heard about it for years (Forrest J. Ackerman frequently ran stills from it in his magazine Famous Monsters), but never had a chance to see it until I got the DVD.
If you go to the internet movie database and click on the names of the performers, you can see that they did, indeed, appear in other films.
Schlitzy “The Pinhead” appeared in four other films, including Island of Lost Souls. That film’s denoument reminds me of that of Freaks, perhaps because Moreau’s creatures really do look disturbingly real.
Johnny Eck, the “Half Man” appeared in three other films, too – all of them Johnny Weissmuller Tarzan films
Daisy and Violet Hilton, the Siamese Twins, actually starred in the film Chained for Life
Most of the others did not appear elsewhere, except in documentaries.
Incidentally, Bill Griffith, who based his Zippy the Pinhead on SChglitzy, recently released a biography of Schlitzy in graphic novel form, Nobody’s Fool: The Life and Times of SChlitzy the Pinhead. He interviewed some of the people who worked with Schlitzy and dug into his genealogy. Well worth the read.
Rather tragically, Rondo Hatton made use of his case of acromegaly to his advantage to appear in 25 films, invariably as the heavy. His condition eventually killed him. He inspired the character of Lothar in Dave Stevens’ Rocketeer comics, and the character (recreated with heavy makeup) appeared in the movie The Rocketeer
Frank Henenlotter’s film Basket Case involves a pair of conjoined twins, represented in the film by models and special effects. This low-budget film had a higher-budget sequel, Basket Case II that featured an entire house of freaks. In order to avoif offense, I suspect, Henenlotter’s freaks are outrageously distorted, and they’re definitely positive characters. There was a second sequel that I haven’t seen.