He beat up the women in his life so racism definitely wasn't his only issue. However is it possible he joined it for the connections/political influence and didn't take part in any racial violence?
The Ku Klux Klan was very active in Missouri in the early 20th century but was generally more of a social group (granted it was a racist social group) than a lynch mob. Harry Truman was briefly a member of the Ku Klux Klan in Missouri for political reasons. He seems to have not been active and may have had disagreements with the local leadership regarding the Klan's position on Jews and Catholics.
It should also be noted that while the Klan participated in and even ordered lynching they were not responsible for all lynching or other violence.
This site provides a list of lynching by state and year. There were several lynchings in Missouri during the time your great grandfather would have been involved.
In answer to your question your great grandfather may have joined as Harry Truman did simply for political reasons, however as a high ranking member it is likely that he participated in lynching or violence at some point but was not likely directly responsible for killing the individuals.
The general consensus on the 1920s Ku Klux Klan is that it was mostly non-violent. Missouri was never famed for being particularly violent Realm of the Invisible Empire, although nearby states like Oklahoma and Texas were undoubtedly the most violent. If your great-grandfather was an officer in the Missouri Klan, I would say it is unlikely that he did order that sort of violence since he was a leader. The 1920s Klan leadership preferred to avoid violence as it gave bad publicity to the order and was detrimental to the movement. But that was only really the case after 1922. Before that violence was much more prevalent.
Most violence committed by early 20th century Klansmen was committed without official approval. But that's not to say it did not occur. It just so happens that most Klansmen would attack people without wearing their robes or identifying themselves as Klansmen.
David Chalmers, Hooded Americanism (Duke University Press, 1981) has a chapter on Missouri if you're interested. For more general information on the 1920s Klan, Shawn Lay (ed.), Invisible Empire in the West (University of Illinois Press, 2004), is a good bet.