I think it would be okay! By trading away the design you already admit you no longer want it and shouldn't be bothered by it being revamped and sold. Seeing the last batch of revamped dreamies I think most of them were far enough removed from the original to count as a unique design. But like paladin said allowing the user a choice whether not they feel comfortable with having the design revamped and sold pretty much remedies the issue, or have it upfront explained that by turning in a design you forfeit all rights to said design.