Does Craft Commerce support multi-channel fulfillment and inventory?
The short answer is, out of the box, no it does not, currently.  Inventory handling is quite basic at the moment, for example.

You could probably deal with a lot of the access stuff via Craft users &amp; permissions, but there's no doubt in my mind this would involve a very substantial amount of custom plugin development work, and I'm reasonable sure no such plugin currently exists.

Commerce is still a relatively young product, so who knows about the future, but right now it would not personally be my first choice for this sort of project.

(You could perhaps tackle them as separate installations and use things like the ElementAPI to push product content between the systems, though, if the key issue is content sharing as opposed to one unified back end).