Remember that home inspectors are not code inspectors. Our goal is to provide our clients with information to make the right decision. So what is the concern with exterior electric panels? Many of these panels are within local code but think about a heavy rain hitting the box .... would it prevent water from entering the box and causing an arc or short? If you have an exterior box consider adding additional protection to keep water from entering the box. Even a simple awning of some sort above the box would provide some protection. Or buy one of the many enclosures that provide adequate protection.
I am a full-time home inspector servicing all of South Carolina.