Unlikely to be a HIPAA violation, pretty standard to get a BAA in place between entities sharing PHI type data. Its spelled out on those HIPAA forms you sign at the providers before they'll see you.

"The Privacy Rule allows covered providers and health plans to disclose protected health information to these “business associates” if the providers or plans obtain satisfactory assurances that the business associate will use the information only for the purposes for which it was engaged by the covered entity, will safeguard the information from misuse, and will help the covered entity comply with some of the covered entity’s duties under the Privacy Rule."

https://www.hhs.gov/hipaa/for-professionals/privacy/guidance...