There is a response on my IMDb query that directed me to an Amazon book Fiorello, A New Musical in which Kaiser and someone who calls herself "Shewolff77" offers a garbled support of Kaiser's account. There is also a one-off review by someone with the interesting name of "Deamon Ferret" (probably an avatar of the two women posting here) in which they claim Sheldon Harnick (lyricist of Fiorello) didn't write the songs.

A Google search on "Sheldon Harnick" "Joseph Toner" comes up with links to various comprehensive works about Broadway plays. It looks like if he did exist he was a walk-on bit player. BlueGoBo page for Fiorello shows he played a "seedy man." Click on Toner's name and it gives a very slight oeuvre on Broadway - two musicals. The last one where he was a walk-on did not involve Thomas. They don't appear to have crossed paths, at least not in what I find so far.

A link to the a page in the Google Book The Golden Age of American Musical Theater: 1943-1965 shows that "Joseph Toner" had three bit parts in the premiere of Fiorello starring Tom Bosley. It's hard to get Toner to show up unless you link him with another name.

I found a link to turn in changes at IMDB. Not sure I filled it out right, but if they take a moment to follow a couple of links I posted they can see for themselves.

SRS