Ah ok, got it, I thought you were going to try to use the Uno and RPi3 for control, doable, and there are a few examples out there, but a lot of rework. Using the Uno and RPi3 together for sensor work should work out very well for you.
At this time, no, I am not using the RPi3 for control. It's connected via USB and has power, but that's about it. I'll post updates as the communications goes along, but the RFD900+ already has pretty good range for lakes and lagoons. The limitation has been my RC transmitter, which is probably around 1000ft.