Yes, they are.
All of our 1.9gHz / DECT office headsets are in compliance.
HIPPA requires that the headset be passcode protected or encrypted.
Our Leitner, Plantronics, Sennheiser, and Jabra headset have 64-bit digital encryption; which is in compliance with the HIPPA standards.
Anyone attempting to listen in on wireless frequency from the calls would only hear a slight buzzing sound.
We have documentation about HIPAA here in Product Support.