No, it really doesn't. Some people cosplay as models or for fun, not out of and obsession with a character. Though I suppose if you want to be a character obsessed with someone from a show or something and have them cosplay as that person, they'd count as an otaku. But then again, otaku is sometimes used as a general term, rather that someone who is obsessed with one particular thing.
It appears as though I hav confused myself @_@