On the March 7, 1937 broadcast from New York, it's obvious that Don Wilson was one of the "Jell-O singers" at the top of the show.
Regular listeners to recordings of the Jell-O programs invariably observe that Kenny Baker sings the jingle, and later Dennis Day, although Baker's tenor is more prominent.
So did the entire cast sing the jingle, or was it a combination of the musicians, Kenny/Dennis/Don/Mary and occasionally Jack?
It seems the most trivial of questions, except that people who listen regularly inevitably want to know. And I don't have the answer myself.
There are some clues, though. For instance, in studio broadcasts in the 1930s and 1940s, the cast used exactly two microphones. Jack and Mary used one, everyone else used the other one. Does anyone really think Don would sprint to the mike after a chorus was finished? So that makes, at the least, Don and the tenor.
On one military base broadcast from World War II, it sounds as if the base glee club is singing it. By then, of course, the Jell-O jingle was a beloved national catchphrase.