I can understand the logic of capturing DV through analog to smooth out the chroma information for keying purposes, but I can't believe that the image in general wouldn't take a hit. DV is compressed 5:1 by the camera. If you then capture it through analog, the NLE, that has no idea that the original material on the tape is DV, takes the analog signal and compresses it 5:1 again (assuming you are working in a DV project).

So the material might be better able to handle keying, but it's already been compressed 5:1 twice. Add any effects or colour correction that need to be rendered, and you lose more quality...