Not necessarily. Grease is too thick and would get pushed around and away from the parts that need lubrication over time, therefore effectively not providing enough lubrication for the spring against the inner wall of the fork tube at key intensive contact areas. Oil moves freely and continually provides lubrication indefinitely all over inside the fork tube. The fact is that fork oil in all motorcycle forks serves two main purposes: 1)Damping - through variably sized orifices controlling the flow of fork oil. The larger the orifice, the more free the flow and the less damped the fork. 2)Lubrication - of fork internals for longevity of parts. And correct me if I'm wrong here....but oil is slick isn't? In this setup it definitely doesn't go into the cartridges themselves. So using subtraction, it's easy to deduce that the oil's function would simply be lubrication in this application.