The answer to the OP's question is a bit more nuanced.
If you actually have permission from the patient to go into their chart, then it's not a HIPAA violation. However, that permission should be in writing, and should be filed in the medical record. Usually, the best way to do this (and especially in Epic) is in the MyChart portal -- you apply for permission to access someone else's MyChart, and once all the paperwork is complete you'll be able to see all the notes, labs, etc. Almost everything is in the portal.
Just having verbal permission is not good enough.
Actually accessing the chart itself, even if you have written permission, may not be allowed by your hospital's local policies. So although it may not be a HIPAA violation, it may still be a problem and violate your institution's chart access policies. Many places will require that you do so through the portal, which is easier to track and control (and also allows the patient to decline to release something to the portal that they don't want you to see).