If you want a theory confirmed, it's best to go to the source of the theory. Case in point: J.K. Rowling and anything to do with Harry Potter.
Recently she confirmed a theory about Dumbledore, now she has answered a question about Hermione and the pronunciation of her name.
See, it appears that before the movies were released, some readers of the cherished books weren't exactly sure how to pronounce names like Hermione and Voldemort - i.e. names with more than one syllable in them.
Apparently, some people were saying HER-MY-OWN. Oh, how foolish and naive we were back then!
So, in order to fix this, Rowling included a passage in The Goblet of Fire just tell everyone how to say the name.
The author confirmed this after being asked about it by a fan on Twitter.