1st you can playback DVCProHD without a card, you would not be able to monitor it to a TV though with the card you have.
I think the idea workflow, if you can, would be to capture the HDCAM footage as DVCProHD and then recapture you HDV tape as DVCProHD also. Don’t know if the amount of footage you have or it the Post House has a HDV deck or camera with HD SDI out. This way you edit in DVCProHD and then take you project back and master that to the HDCAM deck. This may cause you more time and money at this end but it would save on the back end. Plus I think your quality is going to be better than editing and finishing in HDV.
Alternative would be to upgrade to FCS2 and use the mutl format timeline. Capture the HDCAM as DVCProHD, edit in DVCProHD Timeline it will playback with the HDV. render out the final as DVCProHD or ProRes.