I'd have to look back, but these are off the top of my head. AlanScott can certainly fill in the others.
Ben Vereen was of course not in the original company of Chicago.
The song where the nudity famously occurred in the original production of in Hair was "Where Do I Go?" - not "Let The Sunshine In." (though they claim they were just including that song title in the answer for the hell of it - but why, when everything else in the quiz was supposed to be fact?)
Don Quixote was NOT written by Broadway actor Miguel Cervantes. (They left out the "De")
One of the answers was "Pajama Game," but the official title of the show is "The Pajama Game."
I also had quibbles with the clues for a few of the extra credit questions - even though they claim they were just joking around. (See my comment on the "Hair" gaffe.)