Yes, I expect that the VFF will be similar to the position control VFF on the load actuator axis. Whether in force control or position control, the valve has to open approximately the same amount to achieve a certain velocity, so the feed forward will be pretty much the same.
The easiest way to set the VFF is to look at a plot of motion that includes a section of steady velocity, preferably close to the fastest velocity the system will experience during normal operation. Then, divide the Control Output (in terms of percent) by the Actual Velocity. This method is fairly intuitive given that the units of VFF are % of Control Output divided by velocity (% / pu/s), where pu are the position units, such as in. or mm.
This assumes the system is linear, meaning that the velocity is linearly proportional to the Control Output.