Hi, Angela!
Take a look at Walt Disney World's website, where
Hollywood & Vine is described as "Character Dining" for both breakfast and lunch. Dinner, of course, is not Character Dining. If you click "Read More" under "Dinner Buffet", you'll see "Please note: Disney Characters join diners for breakfast and lunch only."
If I were you, I would call Disney Dining at (407) WDW-DINE just to be sure that the reservation time you have secured for "lunch" is, in fact,
lunch. If it is, then confirm with the Cast Member assisting you that characters will be present at the time of your seating. There have, at times, been conflicting information on WDW's website, and it often is a simple oversight that misinformation is present in one location while the correct info. is present elsewhere. At those times, I call Disney directly. If you do so, too, and provide the CM with your reservation time or Confirmation #, I'm sure you'll put your mind at ease once and for all.
Have a wonderful trip, Angela! Be sure to send more questions as you think of them; we love to help!