You also have to book this by phone - you can't book it online. It's not automatic with the restaurant reservation - you must request the Fantasmic package. They'll take a credit card number to guarantee the reservation - there's a no-show fee if you don't cancel and don't show up. You will likely also not get a time past 4:30, and that depends on how early or late the Fantasmic show is. All package reservations are very early.
I also wouldn't call it VIP seating. It's reserved seating, and you don't have to wait 2 hours in line, but the view is no better or worse than anyone else gets.