Can I informally ask the special session organizers about the paper's decision?
Yes, you can certainly ask, but you may not get an answer, especially in the time frame you need. So, when you ask, say why you need the information. 

But even if you don't get an answer, you can list the paper in your CV as "submitted, awaiting decision", so that you get some "credit" for it. But, since decisions about the postdoc won't be made for a while, anyway, you can probably update your cv when you learn more.