They are required to give you a 135.293(b) before you act as SIC on 135 trips. If you do your training in the aircraft what you'll then do is take a copy of your checkride and a completed 8710 to the FSDO and they'll issue you an 'SIC type' on the spot. The company is doing you no favors here, essentially you're paying for your 135 training. I can't imagine what sort of other contracts and monetary obligations you'll have to this company in the future as you start attending sim recurrents/upgrades etc...