Can I connect multiple brushless motors and ESC's to a single GND in Arduino Uno?
In your diagram the power supplies are wired in series 'back-to-back' so the top ESC is only getting the difference between their voltages. Most ESCs have their signal ground connected to battery negative internally. If the signal grounds are connected together and there is a significant voltage difference between them (eg. because the power supplies are in series), a large current could flow which may burn out the wires and/or destroy the Arduino.        

Each power supply should be wired to each ESC separately. The ground wires of each ESC signal lead must go to Arduino ground. Powering each ESC from a separate PSU ensures that motor current won't try to go through the signal leads. 



If you want to power two ESCs from the same PSU then make sure that the negative battery wires are firmly connected to the PSU with short thick wires. If the negative battery lead of an ESC becomes disconnected then it will draw power through the signal ground wire from the other ESC (not good if your motors are drawing high current!).