No,
the codec would be determined by the A->D converter. Vegas simply receives a DV25 data stream either as recorded on the tape (for capture from DV) or as encoded by the converter.
If your analog capture device is internal then there is a good chance that it has a selection of codecs included. VidCap will often let you select from this list.
But, as Bob said, if you're analog converter is an external analog -> DV device, then the codec is within the converter and VidCap will only see the DV stream with no further processing available.