I never thought of Dionne as a man's name esp. spelled that way. I think of Dionne Warwick as well!
As for Mildred, sorry, but I don't love it. However, as a middle name, not everyone will have to know what it is and they do get used rarely. I do know several people though who absolutely despise their middle names. One is a woman whose middle name is Elvira. She is absolutely embarrassed by it and will not tell anyone what it is. I only know because I married into the family and someone else told me. She would not tell me. Another is a guy whose middle name is Francis. His ears turn pink over it. He hates it. I love timeless names but not names that are "old lady" names. That's just my opinion though and you should go with what you like.