There's no real difference between HDMI and DVI cables, certainly nothing that would in any way affect "reception" of any kind. Most satellite boxes use HDMI. There are some boxes that have software bugs that affect the DVI/HDMI outputs, but that has nothing to do with the cables.
If you see a "big difference" between component and DVI outputs on your DVD player, it's likely due more to the component cable you are using or the player itself. Your player should have a setup for picture adjustments on the component outs, (DVI does not), you may have them adjusted poorly. If you want to compare the 2 outputs, be sure that the picture adjustments are correct for that purpose. Same for the monitor end, you may have them adjusted differently. But in any case, HDMI/DVI is a superior connection, and should be used for the best quality source, which is deffinitely HDTV.
BTW, Dish did not buy the VOOM service, they are simply providing the VOOM channels by subscription. The satellite they use is WAY too low in the east, and is nearly useless in the northwest and western states. They also charge $100 for the extra dish install. If you live in the west, you will see a lot of weather related problems on that sat's reception, even if you do have a clear view of it. AFAIK, it's the same sat that VOOM was using, which I am personally familiar with. It takes very little weather to block it in the southwest USA.