In their site's forums... And thats merely because no card creator want to be linked with V-Card made by fans... (and for legal purposes, if a card designer really made a copy of a dream card made by any fan, they could use it 100%, since they OWN the rights of the game). A real and practical example of this is Magic the Gathering... if you have a ton of dream cards, they are MTG dream cards... anywhere, everywhere... I even know a couple of friends that run a software to create virtual cards... and the site still up, after so many years, so Wizards of the Coast it's not very concerned with that...
Listen, it's as stupid as this: "Oh no, don't create any dream cards that we might see, copy, print and SELL FOR MONEY!"
Copyright issues are severe, when you steal something to make profit out of it, when you claim you are the owner or creator of something you are not... Then copyright can totally punch you in the face...
They state the policy of "no dream cards" among their websites, not fan websites... One of these days you have Chris Tolkien (or whatever his name is) forbidding any fan to write a fan fiction or an rpg about Lotr... "Oh, sorry, you can't... I probably will have that idea in a near future so you are not allowed to write it..."
Right now, even if you do any DC for Lotr TCG, what would Decipher do? "Oh, they stole ideas we could use... for future sets... that we are not allowed to do anymore..."
Seriously?