You can use Hydraulic servo valves and linear scales, Bosch actually built a CNC machine using Hydraulic cyclinders this way.
There is also a company that I believe is still in existance that developed an interesting cheaper alternative, Instead of the costly servo valves which are operated by the Servo card and move the spool back and forth proportionaly, with a electro-magnetic lever, these valves are very prone to oil contamination and require very fine filtering, also costs in the $k's.
This development was to use stepper motors to move the spool under any stepper controller you want to use, Usually linear encoder is still used for precise positioning.
BTW Avey used to make a mill/drill that had a Hydraulic cyclinder for the Z and the feed was a binary combination of 8 flo valves, quite the set-up.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.