Are you sending the data from the "accelerometer" to the "Dynamic Broadcaster" using the UART interfaces? Why not directly broadcast from the accelerometer chip?
Assuming you want the data routing through both chips:
Have you tested to make sure that the UART wakes up the "Dynamic Broadcaster" when it interrupts? I thought that the UART peripheral is asleep when the chip is in deep sleep mode. Try skipping the "EnterLowPowerMode" function and see if that increases functionality :)
Another thing to check would be to make sure that the RX of each UART is connected to the TX of the other UART and vice versa.