Gear type flowmeters could definitely do something to paint pigments, as the meshing of the gears causes very high shearing forces to be applied to the fluid. Less of an issue with vane types, less yet with piston types. What is worse with any of these types of meters is that the paint can harden and clog the meter, or harden along the endplates/seals and cause excessive wear and leakage. There are other, noncontact metering technologies out there (simple orifice plate and dP transducer, ultrasonic, coriolis force (or vibrating U-tube), magnetic). Spend some time on the GlobalSearch site and look at what is available.