I believe it does not have an effect on Yahoo search rankings although someone correct me if I'm wrong.
Most of my traffic comes from google searches And that includes all my sites, even those that I don't promote on Yahoo answers. So I would draw the conclusion that Yahoo answers has no effect on my Yahoo search traffic
I don't think so that this will help you in ranking but if you are answering questions regular bassis related to your niche than you can get good traffic .
It will not effect on yahoo search rankings but you'll able to get traffic and backlinks from it (Yahoo Answers).
It will be beneficial to submit your link to yahoo answers because you may receive some traffic from it.