Yes you can connect all the servos to the rx. Some servos do not like 6volts, but those are generally low end servos like the Jr Sport ST47's and the Futaba 3004's.
In my H9 1.50 p-51, I'm using mostly Jr DS821's. They are digital servos and have very nice torque for the price($29) and have no problems with 6v. Most Hitec servos are happy on 6v as well. If you have servos that chatter on 6v, then you can install a voltage regulator to lessen the voltage reaching the rx, but shouldnt be needed unless using low dollar servos.