You've basically answered your own question, as follows:
You are not using iCloud, nor are you using iTunes on a computer. These are the two vehicles Apple primarily uses for sync.
Therefore, as you said, any sync that occurs would be in the hands of Yahoo, your email provider. So it's really a question for them. I would guess syncing is likely, but that's entirely up to Yahoo.
Currently Being ModeratedJan 19, 2013 9:04 PM (in response to sberman)
Thanks for the reply but still no answer... I am actually trying to find out how Yahoo contacts works with iOS devices, whether they are merged or one side always has higher priority than the other side... Since I don't have computer to backup existing contacts, I must get everything clear before doing that, so prefer anyone who has used Yahoo contacts shares his experience.