At zero G, you're likely to not have any hydraulics going into the pump...
I know that you get a slight hydrolic failure when pulling zero or negative G's. I have felt it from the certain type of work we do, when pushing over a hill trying to fly the same heigh AGL the whole time. When I wanted to turn around during that push over I had stiff controls like a hydrolic failure. But it was only for that one second until the hydrolics pumped through again.
So here's the question. Why doesn't the hydrolics warning light or horn come on at that instance? Because surely that is almost like a hydrolic failure.