Is the hydrolysis of ATP to ADP reversible?

Yes, the hydrolysis of ATP to ADP is reversible. 

ATP (Adenosine triphosphate) is made up of 3 phosphate groups that are linked to each other by high-energy phosphoanhydride bonds. During hydrolysis – a water-mediated breakdown reaction - one phosphoanhydride bond is broken, releasing one phosphate group and leaving behind a molecule of AMP (adenosine diphosphate), which is made up of 2 phosphate groups. 

The reverse reaction adds a phosphate group back to AMP and regenerates ATP.