A Be20 can be operated Single-Pilot under 135 IFR regs as long as you have an approved and operable auto-pilot. Now, since the above mentioned Ops' Specs say you need the SIC and it's authorized, then yes, they are now a required crewmember. As mentioned before, just log it as Total-Time, not SIC. SIC in Be20 means about Jack-Squat, but the Total-Time is what you need!