I haven't done a late breakfast here but I have done last breakfast seatings at 'Ohana, 1900 Park Fare and Tusker House. At 'Ohana and 1900 PF it's easy because there's no lunch seating so they know that everybody who's there is there for the character breakfast. At TH I was nervous because they were late seating. The CM at the entrance assured me that the characters would see everybody who had a breakfast ADR. I think I figured out how they can assure that. I believe that there's a break where they don't book ADRs between the breakfast and lunch seatings. TH cleared out while we were eating and people weren't being seated at those empty tables for a while. Shortly before we left, as they were putting out the lunch foods on the buffet, they did start seating people again but the restaurant at that point was pretty empty (our meals always take longer than for most people becuase we have food allergies to contend with). The few of us that were left had seen the characters.
I would assume that H&V would work similarly to how TH worked.