All the Y does is expand the slots in the receiver. And all the voltwatch connects to is the battery supply + and - . So, you can connect to that anywhere as long as it's in the circuit (which means NOT the charge jack because when the switch is turned on (presuming you use a switch), the charge jack is OUT of the battery circuit.

So, a Y, paired with a servo is just fine. Heck, you can also parallel up a second battery that way, again, through a second switch is best.

CGr.