Unfortunately, securing data on the backend gets one about 5% of the way to HIPAA compliance. Does one have e.g. a written risk assessment and mitigation plan? No? Insta-violation.
Full transparency - I'm one of the founders of Catalyze. Yes, we do. We've been through a couple of 3rd party HIPAA audits. You're absolutely right - HIPAA is more than just backend security. All our internal policies are documented here (http://catalyze.io/policy) and their mapping to HIPAA is documented here (http://catalyze.io/hipaa).
I do not doubt that you are on top of things. Just pointing out that your customers also have to be on top of things, or it is unlikely they will be found compliant if audited.