I know one of the of the pilots. It would appear to me that the King Air position of the SIC is for insurance purposes only. Best guess would be that they use the SIC in lieu of an autopilot. They appear to be rather straight forward. The SIC jet pilot times are what I was seeing prior to 9/11.
It might be for more than just insurance. The King Air 200 Spec and Data sheet requires two crew memebers for 135 operations, but only one pilot for 91 operations. I guess it depends on what the company is using the King Air for. Hope this helps.
The only reason an SIC may be required in a Part 135 IFR Operation is if there is no autopilot or it is inoperative. Most operators that have a certified autopilot get approval to use an autopilot in lieu of a SIC. But regardless of the equipment or authorization there is no restriction from using a trained and qualified SIC in 135 ops regardless of the aircraft type.