I don't have a way to check this after the fact, but Adobe has a product called InCopy that works with InDesign; it lets you synchronize between multiple layouts of the same text (ebook, paperback, and hardback for example).
Acrobat "pro" also has a text compare function; you could, I suppose, make a pdf from your epub file (by breaking it open as html and then using print to pdf from a browser) and then use the compare from the pdf made from the epub. You probably have to do this chapter by chapter since in the epub, each chapter is its own html file. Sorry, that's the best bad option I've got.
Acrobat "pro" also has a text compare function; you could, I suppose, make a pdf from your epub file (by breaking it open as html and then using print to pdf from a browser) and then use the compare from the pdf made from the epub. You probably have to do this chapter by chapter since in the epub, each chapter is its own html file. Sorry, that's the best bad option I've got.