I know the afromini controllers (a smaller(!) version of this board) has onboard regulation with a tap for powering external electronics like your RX, but from all I've read about the Naze32 boards, up to rev5, the high power bus is still shared among the interfacing connections, without a regulated tap. that means the harness going to the RX and to the ESCs are tied together and there is no 5v regulation -- just 3.3v regulation.
There's a better-than-even chance the regulator for the 3.3v bus is more than able to handle 12v (they're usually good up to 18) directly, but I doubt your receiver would be so tolerant. If your receiver can run 3.3v under 100ma (pretty common for satellites) you should be good to go.
Otherwise, if your ESCs have UBECs built in, why waste the extra weight on an external UBEC? running power off the ESCs is the simpler way to go.
BTW, there *IS* a battery sense port capable up to 6S, but it's a resistor limited A/D port -- it reads voltage, but can't be used for powering the device.
Edit:
On second glance . . . scratch the second regulator on the Afromini -- it also has a shared unregulated high voltage bus. Also, the note on the Afromini leads me to say, use high voltage with caution -- the earlier versions had a 3.3v regulator limited to 5.5v, and the newer versions are limited to 16v (not 18v).
Unfortunately that still leaves the regulator on the regular Naze board undefined, so proceed with caution.