OK, first I do not know what a barrel pump impeller looks like, so I do not know what direction I would expect the water to rotate in the TopLeft pump image.
If the rotor geometry inside the MRF, rotates CW, would I expect the water to rotate CW 
Are you saying that I cannot have a +Z axis of rotation and a -ve MRF direction (that may be my little brain issue here)
Even if that were so, I still need to know if my CCW Right Hand fingers were pointing in the direction that the rotor would spin or in the direction that the water in the MRF would spin relative to the domain, wouldn’t I …