The similarities between some contest entries and the recent Sackboy DLC were pointed out on Sony's LittleBigPlanet General Discussion forum, where users debated whether or not Sony had in fact copied the designs, and if so, if it had a legal right to do so. While some users pointed out that the terms and conditions of the contest clearly indicated that all submitted materials became the property of Sony, to do with as it pleased, Sony took the matter one step further and denied that any copying took place at all.
"This was always going to be a possibility when we ran the costume competition - releasing new costumes which are similar in theme to ones that were entered," a Sony community rep wrote in a message on the forum. "Here's the fact of the matter, the art team who are responsible for designing new original (ie., unlicensed) costumes were involved at the very final stage of judging, by which time the number of entries had been whittled down to 10 from each batch of entries (Europe, Japan, USA). If at any time we take inspiration from a costume competition entry that didn't win overall we will contact the creator directly."
The designs posted are undeniably similar to the DLC releases by Sony, but the Sony rep has a valid point: Overlap between Sony's work and that done by fans, given the sheer amount of material being created, is almost inevitable. It's unfortunate, but I find it hard to imagine that anyone at Sony or Media Molecule would intentionally rip off contest entries; even if the contest fine print grants them the right to do so, the potential backlash against such a move would more than negate any benefits gained. The costume designs in question, and the corresponding DLC from Sony, can be seen here.