Basically ZeroShell is a Linux distribution, just setup so that you don’t have to get to the shell to set things up. At least usually you don’t have to get to the shell. 🙂
So I’d interpret your question as can Linux support your needs. You’d have to have some fairly powerful hardware… And even there I’m not sure. I tend to think of those kinds of data rates and session numbers as more appropriately handled by systems that have hardware capable of CPU offload for the basic routing functionality. But I could be wrong. You might try directing your query to some forum where Linux is used in heavy duty traffic management environments. If the answer is yes, Linux can do it given some minimum set of specifications on the hardware then ZeroShell can do it too.
I think most of the people using Zeroshell are using it in SOHO environments.