Yes, SDK functionality has been verified using a different model of modem.
Have tried two different MC5728V modules on our hardware and both behaved the same.
On our hardware, MC5728V is connected via standard minicard connector (mPCIe) and communicates via USB signals (not UART). When connecting with PC, the MC5728V is inserted into Sierra EVK and connected to PC via USB.
Not sure what you mean by extra hardware pin - we connect to all appropriate signals defined on the MC5728 module connector, including all UART signals, W_DISABLE, RESET, all power, all gnd.