I've heard from many that the FX1 outputs MPEG2 in HDV mode during capture. If this is the case, I've also always heard that MPEG 2 was a rendering format only and was not ideal for editing. Anyone have any clarification on this?
Using an intermediate codec is probably the way go for editing with Vegas.
However, my understanding is the MPEG in HDV is different from the MPEG in a DVD. However I don't know how it stands up to multiple renderings. There is raw HDV available for download, you can search this forum and play with it.