Yes, Elite and Gold annual pass does include access to the LEGO Festival! The event dates are:
May 3-4, 10-11, 17-18, 24-26, 31
June 1, 7-8
However, please note that Bronze Passes do not include access on May 24-26. If you have a Bronze Pass and wish to visit on the excluded dates, you will need to purchase an additional admission ticket.