You can use any number of objects for a hover area, in addition to buttons. For example, you can use images and shapes. I often use transparent shapes when I want to have different hover areas over a graphic or want to have a hover area over a text box (since text boxes don't let you do mouse enter commands.) For usability purposes, I would make sure your hover area does not "look" like a button. Intuitively, people want to click buttons instead of roll over them. So I prefer to use something that is flat rather than something that looks 3D like a button.
