Rule 1, don't ask, don't tell. If you ask, the answer will always be no. Sometimes after you ask, you may get greeted with metal detectors at the entrance or signage that does have force of law when prior to asking there was no such physical or statutory prohibition. While the zoo may sponsor concerts, I would suspect the prohibition for CCW would apply to the building the concert is confined to and not the entire zoo itself unless it meant the legal definition of an "outdoor music festival."Supposed to be in the top 10 of best zoos in the US. Went there once packing only curiosity, most of the critters looked like they are doing hard time in Walla Walla state pen.
Try admin at this URL for CC questions:
WPZ Contact Information
Place used to sponsor concerts too, which is a no-no for any CC, been a while.