In my opinion, if you're hosting the contest, you should never participate in it. I just posted my own haiku, so hopefully a couple more people will post.
Fan fiction isn't popular because it takes a lot of time and commitment in order to make it good. A lot of people don't realize just how much work it is to make a story. So, they start and never make it past the second chapter. My hope for the section isn't to have a lot of fics, which we already have a fair amount, but rather to have a lot of people in the writers' lounge discussing various topics and helping new writers out. If that happens, a community will start to form. When a community forms, you have friends, and friends feel more inclined to reading each others' fics and more reviews happen. It's a cycle I'm trying to start up over time.
Competitions will be a key factor in building that community because it almost forces people to interact with one another. I don't want any long-term competitions right now, because that takes time and effort which some people might have in the beginning, but not towards the end. I like your haiku contest because haikus are relatively easy to make (ignoring quality) and it doesn't require long-term commitment. If competitions are going to be successful, they have to be short and sweet.
I also sent the advertisement request and I'll tell you if it's accepted or denied.