After the "Maui Miracle", the owner made it mandatory that each and every flight operates with an SIC. They updated their manuals, and the FAA signed off on it. So all SIC time is counted at Mokulele.... if there's no FO, they can't operate Part 135.
That's how they are different from some of the other Part 135s; on Mokulele its mandatory whereas many 135s are still flying under the single pilot requirement with optional SIC.