I am pretty sure that Yahoo still uses at least 49% of its own search technology provided by their Gemini system, at least on Desktop devices. The deal Yahoo and Bing talked about was mainly regarding PPC ads, I believe. Yahoo has to serve 51% of its ads to the Bing network under the latest contract - something like that.
Regardless, ranking on Yahoo by using a Yahoo-related product is still applicable today.
Anyway, I was basically saying that you should consider
1. Answering questions on Yahoo Answers that are relevant to your market.
2. You have to answer enough questions to get you to become a level 2 participant. You get that by getting "best answer" votes a bunch of times.
3. Do this with multiple accounts and answer questions that are most relevant to your market or your client's market. I would suggest you do this with a wide variety of markets / Answer categories because it gives you a solid network of do-follow backlinks once you have level 2 accounts. You take advantage of this by asking your own questions and then also answering your own questions.