The FourPaneViewer uses vtkInteractorStyleImage, which is a “camera” interactor style, which means that orienting the camera is the responsibility of the interactor style. When using this, it’s best not to call SetViewUp(), Roll(), Yaw(), etc. on the camera yourself.
Instead, use interactorStyle->SetXViewUpVector(ux, uy, uz) and interactorStyle->SetXViewRightVector(vx, vy, vz) to adjust the coronal slice orientation. You can choose whatever you want for (ux,uy,uz) and (vx,vy,vz) as long as they are orthonormal.