Yes. Even if the business or a public program has a “no pets” policy, it may not deny entry to a person with a service animal. Service animals are working animals, not pets. So, although a “no pets” policy is perfectly legal, it does not allow a business to exclude service animals.
For additional information, take a look at the following resources:
FAQ: What if a service animal barks or growls at other people, or otherwise acts out of control?
FAQ: How can I tell if an animal is really a service animal and not just a pet?