I dont think so. I tried to use it before but it doesn't help me a lot. Besides Yahoo Answers is not a DO FOLLOW.
Yes I confirm it works. My suggestion is to ""optimize"" your answer in terms of keywords (I'mnot talking about keyword stuffing which is not necessary.
I've seen in the SERPs that yahoo answers get indexed and are sometime high in the SERPs. I would optimize the question/answer.
No it doesn't really help organic ranking, but YA! has a lot of traffic and questions tend to appear high in long tail organic searches.
One strategy is to work on that yahoo answer page to be on top of SERP, then that would bring traffic to your site.