Keanu Reeves was barely recognizable at the Public Theater Gala in Central Park on Monday night. He showed up for Shakespeare in the Park’s “The Merchant of Venice” and lounged on a bench outside the Dela corte Theater looking skinny in an old T-shirt, jeans, beard and sun glasses, sparking many well-heeled guests to say, “Is that really Keanu?” Making a similar low-key entrance was the show’s star, Al Pacino, who arrived in shades and a red bandana and later got a standing ovation after his performance as Shylock. Other guests included Kevin Spacey, Naomi Watts and Liev Schreiber, Lucy Liu, Amanda Peet, Harvey Keitel, Kate Walsh and Sam Waterston and “Glee” heartthrob Jonathan Groff, who starred in the 2008 Shakespeare in the Park production of “Hair,” plus “The Sopranos” stars Lorraine Bracco, James Gandolfini and Edie Falco.