Nope.

And here's why: When you waterproof the shell of a down bag, you increase the possibility that the condensation is going to form INSIDE the bag, in the down. Wet down doesn't do a very good job of keeping you warm, so that's a bad thing.

You can sleep in a bivvy bag, which is more or less waterproof. And then your down bag won't form quite so much condensation on the inside. But it will usually form condensation on the outside...and since the shell isn't waterproof...

This is why tents were invented.