It is possible to use a hydraulic ram with an air cylinder to generate the force needed to displace fluid. While this type of system can generate a lot of force to push any type of fluid, it is limited in speed and accuracy. Depending on the size of the system, it will take time to charge and discharge the air cylinder. The closer to the end of the stroke you are, the longer it will take. Also, there is still energy in the system when the pressure is removed from the air cylinder. This results in fluid drooling from your output port.

I would recommend using some sort of valve on the output port to control the flow of the fluid. The type and size of valve is determined by the type of fluid and flow requirements that you have. This will increase the accuracy of the amount of fluid you are dispensing by shutting off the output and reducing drooling. Using a valve also increases speed by allowing you to keep the air cylinder continuously energised and using the valve to meter the dispensed fluid.