Xbee traffic/bandwidth limitations for a real-time-ish application
Depending on how much data is actually sent every 200 ms, this can certainly be feasible for a 4to1 network.  I've done this with 8to1 networks with a 10 Hz update rate, sending about 20 bytes every time.  It works like a charm.  The xbees come in different flavors, but in general you can get receipt acks at the xbee level (if in API mode), or you can simply implement your own at the application level.  Depending on the configuration, the xbees will attempt a set amount of retries on their own.