That's a great question. The current answer is no, there is not a built-in Emma function that would let you share lists between sub-accounts that you manage. You would need to import them into each sub-account as you would any normal list.
The good news is that I can confirm we are looking into building a feature that would allow a workflow like this. We've been tracking this type of feedback and I can definitely see the use cases for being able to share and manage audiences at the admin level.