I know scythes have been used in combat, but as far as I know it has been used by peasants who could not afford a real weapon. Surely an elite marine could do better.
Anyway, it is an impressive army you have and I hope we soon see a group picture.
I think you are right that the use of a scythe would have been limited to levied or revolting peasants. However, in the diversity of medieval weapons, the difference between an agriculturally influenced polearm, such as a fauchard, guisarme or bill, and the halberds and glaives carried by elite formations is problematic. Even Oakeshot lumped them all together as staff weapons. So I'm not sure that a men-at-arms who had been tripped by a bill and then had the point stuck through his eyeslit or up his nethers would agree that it wasn't a real weapon

Still, as you know, these have scythes because they are the elite of the Death Guard and their boss looks like a Pratchett-esque version of Death, scythe and all.