The server will need a little more for Flash players, because it's generating the map output whereas DS does all that on the client end after only getting some minimal updates from the server.
The server is generating the graphical output seen in the map control for each flash client?
In the DD/DS model, the server only sends each client info about turfs in its general area (it sends a bunch at once, and only refreshes it needs to), objs and mobs within viewing distance, and a handful of other items like anything in a statpanel in inventory. So already a game that's segregated so different players are on different maps wouldn't be sending players info about each other.
In the Flash model, the server builds the map on its end entirely and sends out the info on what to display. This would be unaffected by whether other players were visible on the same map or not.
We haven't given any consideration to server changes yet in Flash. I would assume it's possible, but we'd need to have some kind of way of sharing resources intelligently.