While there are basements throughout Disneyland for the cast to use as break rooms, I've never heard of any of those spaces being built to bomb shelter level. Even with only 18 rides available on opening day they expected about 15,000 people (it ended up being 28,154). They reached 1 million visitors within a few months. Trying to safely house that many people would require a space almost the size of the entire park and certainly couldn't support them for any length of time. Walt Disney World was built with a maze of tunnels underneath, but those were meant for easier movement of the cast members. So, while Disney parks do have security and safety measures for large scale events (the parks were evacuated in under 30 minutes on 9/11), they don't have specific bomb shelters.