Yeah.. you can do that. There are some that are not labled as such. The power input on the DX7 receiver is. But, on all RX's, the power + and - are all "linked" or bussed together so that the power applied to one applies power to them all (servos) including, of course, the RX.

Just make sure you get the signal connection to the signal pin for the servos and don't get the battery backwards and apply the power to the signal pins, it won't work that way. Airtronics color codes their signal pin blue, where JR does in orange. I thing Futaba is white. The normal red is battery + and the black is battery -. For JR, the battery - is brown and the battery + is yellow, I believe.