Sidney's life as a male name goes back for centuries. As a boy name for today, it's vintage but not unpleasantly so: where I live, anyway, it was never popular enough to feel overused. I think it would be fine.
I know one woman, born in the early 1940s, whose mn is
Sidney. Her father,
Sidney, was fighting in North
Africa at the time, and she was named after him in absentia. Her fn is
Jennifer.