hey, so last year i heard that you could only enter anime characters into costume contests rather than characters from webcomics, and other things.
if this isn't true then disregard this whole thred.
Well, no rules have been posted yet for 2013...
However, in the past the "costume judging" portion of the Cosplay Contest has discouraged non-Japanese animation costumes. With that said, there was no such discouragement of the "skits" portion of the Cosplay Contest.
I think the primary thought was that Kumoricon is an "anime fandom" convention, not an "Internet meme fandom" convention. Whether or not this continues is entirely up to the board of directors and the voting membership.
Kumoricon does do a pretty good job incorporating other types of fandom into the convention (the Doctor Who panel comes to mind). Personally, if someone wanted to do a non-anime costume contest I would suggest they contact Jaki Hunt and offer to put something together. Maybe something could be worked out...