How to measure a signal that uses a virtual ground using Arduino
You should be able to connect the virtual ground at the midpoint between the 2 batteries to the ground on the Arduino - as long as you are using batteries and not a power supply and there are no other connections between the two circuits that would cause a current loop. 

An Arduino analog-to-digital input pin can only be connected to a max of 5 volts, so you will need to divide the output of the amplifier to fit in this range. A resistor-based voltage divider with 2 equal resistors will bring the 0-9V down to 0-4.5V, which is a good match for the Arduino. 







simulate this circuit &ndash; Schematic created using CircuitLab