In the spoiler review, it mentions the trio appears towards the end. I hope they did not use those horrid voice actors from HE! Here's what it says:
"Ron, Harry, and Hermione swoop in aboard the dragon to rescue everyone. They’re on their way out of Gringotts, just as they were in the film, but come to our aid in the process.
The group look and sound great, even though their representation is (presumably) computer generated. They did not film or record anything new for this attraction, but it is unnoticeable. We follow them out after they have saved the day and the experience ends back where it began."
Since they "look and sound great", perhaps they just used footage from that scene in the movie?