cannot speak explicit for the airbus, but on the bae146 nosewheelsteering has to be off during any pushback . if not and the hydraulic system is pressurized the hydraulics would try to counterreact when the tug starts to make a turn .
this could/would damage the actuators.
on the bae there was a pressure relief to prevent destroying the whole actuator in case the nw was forgotten to switch off. but when this relief was already pushed no hydraulic pressure will build up and you are without nosewheelsteering so it has to be ckecked.
i quess its similar to the airbus,
normally the pushback supervisor will ask to confirm hydraulics are off / nw off before they start the push.
cheers