Google does not agree that Zappa was strictly tonal:
"Burnt Weeny Sandwich":
The album includes atonal pieces like "Igor's Boogie" and "Kung Fu," which is a 1960s example of his use of atonal music. “
some of his orchestral compositions also include atonality
my favorite Atonalist has to be Sun Ra… saw him with the Arkestra at Norma Jeans night club in the early 80’s.. best music I’ve ever witnessed live.