I was only thinking of the module because I figured it ws regulated already to either 3.3 or 5 volts, I would think. Either might be enough to operate the Rx. There would be no need for a regulator but I do like your idea of using the charging jack too. Then again, a fully charged NiMH 8 cell is about 11 volts. Can the rx take that directly? it would be perfect to use a high voltage Rx and just pump that in directly.
I guess there is more than one way to skin a cat...
Looking forward to your final solution,
Frank