Depends on a few things...
You need to know the displacement of the pump per rev, how may revs you will run it at, is it a variable output or fixed displacement?
That will let you know how much flow of oil you will have available.
How fast do you want the motor to turn? that will decide the size of your motor relative to the pump capacity.
How much power do you have available? What pressure will the pump generate? This will give you the power / torque available to the motor and will assist in choosing the correct motor type for the application.
Valving? Depends on the pump and relief valve arrangement and whether you want the motor stopped or able to freewheel.
If all that makes sense carry on, otherwise look for a hydraulic engineer.
Orange...cause it makes me look like I know what I'm doing!