Can an Aura which was not cast be attached to a permanent with shroud?
Yes, they may. The cards you mentioned returned those Auras to the battlefield, so only 303.4 applies here. It should also be notes that the aura must enchant a legal object (i.e. Auras with "enchant player" must enchant players, auras with "enchant a creature you control" cannot enchant noncreatures and cannot enchant opponents creatures, etc)

Aura spells (i.e. Cards cast from your hand, and added to the stack), do require a target. It is unfortunate that they are the only spells that target, without "target" within the rules text.