Hi Chris,
The dab unit is within the head unit, so unless you change to a RNS510 with DAB (very pricey) then you'll lose the dab functionality.
The Bluetooth is a separate unit, and should work fine, although you may need to fiddle with some wires for the mic, as I think the mic needs to go through the head unit for the RNS but not the RCD (when I installed my Bluetooth the loom was wired for an RNS and I have the RCD so I had to disconnect the microphone in and out cables from the connector and solder them together. You might need to do the opposite when moving from the RCD to the RNS)
Hope this helps, this is to the best of my understanding anyway!
Cheers.