APRN in a supervisory role

Disclaimer: I know zero about scope of practice laws in Hawaii.
However, I believe you may be confusing scope of practice (which determines what a provider may legally perform) vs incident-to guidelines (who the bill goes under).
For incident-to, one of the guidelines is the supervising physician must be onsite and immediately available. If all of the incident-to guidelines are not met, the service is simply billed under the PA. Under incident-to, both APRN and PAs are mid-level providers and cannot be the supervising physician for each other. Additionally, not all payors follow incident-to and some require the rendering provider to be the billing provider regardless.
*IF* Hawaii requires under scope of practice laws (NY does not) that a PA must have a supervising physician immediately available at all times, then the PA should not be treating patients if the MD is not available.