I don't think anyone has tried this with Ubercart. I think a little custom code would allow you to use Ubercart to sell domains, but Ubercart is not really set up for billing. In the future we will incorporate recurring billing, but that will only work for you if you bill your customers the same amount every month, and will still be sort of hackish. Most hosting services charge extra for bandwidth etc. . . and I don't see this working very well with Ubercart.
Peace,
Andy