Connecting DAC output from Arduino Due to another arduino
The inputs to Arduino pins are CMOS inputs, and present very high impedance.  (There is a tiny capacitor on every CMOS input, and the only current into the input is the very small amount needed to charge that capacitor.)

You don't need resistors when connecting inputs and outputs (digital or analog) between Arduinos. Should be the same with Raspberry Pi GPIO lines, or any other CMOS devices.