No. The GPS Receiver only receives standard GPS signals. It does not receive Differential GPS (DGPS) signals. If the user requires DGPS input, the GX3 will accept DGPS via an external feed and in the case of the 3DM-GX3-45, incorporate it in its Kalman filter processing. To be clear: the on-board GPS will be bypassed in favor of the external GPS.
Wikipedia GPS: http://en.wikipedia.org/wiki/Global_Positioning_System
Wikipedia DGPS: http://en.wikipedia.org/wiki/Differential_GPS