Connecting an Arduino to Raspberry Pi
Yes, what you are trying to do is possible, just connect the GND of both to each other. 

Also, instead of using two power supplies you can use just one 5V power supply and connect VCC and GND from both to each other and you will be fine. (Amps will depend on your specific power consumption)

The on-board voltage regulator on arduino might not be sufficient to power 3 servos, you are better off using a 5V power supply and connecting servos to VIN instead of VCC.