Angela and Hodgins are a case of opposites attract. They met while working together at the Jeffersonian. She's a free-spirit artist, while he loves bugs, plants and rocks. Their differences only make their relationship stronger.
The impossible becomes reality all the time. Ideas, and memories, and love. You can't hold those things in your hands, but it doesn't mean that they don't exist. So, why not spirits? And why not Sweets? You don't have to believe. I get it. But you don't have to dismiss the possibility, either. No decent scientist would do that.