I think it would depend on what you mean by genderbends. If a character changes gender and there are both versions of this character around (can switch back and forth) in the fic, I would be a little hesitant to call the genderbended version an OC. But if there is the only genderbended version (born that way, or cursed from pretty much the beginning, or the change is permanent), and he/she is otherwise thinking/reacting in a way more like the gender he/she currently is than like his/her original (canon) gender, I would probably feel that character is more of an OC. As for the permanent change scenario, if the character is desperate to find a cure to change back, I would not say he/she is really an OC either.

(Sorry, I ramble, when you're probably only looking for a simple yes or no. Not sure if all the above would really be applicable, either, since...well, since, as you said, genderbends are apparently part of occhallenge, so maybe I've been misusing/misunderstanding the term. In any case, I'm sure genderbended Wataru would be very interesting.)