I shoot raw and jpg and import both into LR. I set the jpg as B&W in camera as I can then compare colour to B&W for the same image in LR. I also prefer shooting and thinking in B&W so my screen images are B&W. whilst the histogram in camera and clipping are jpg based seeing blue and red on B&W is easy.
Interesting, but I'm unclear what advantage there is to setting the camera to capture both RAW and JPEG. "Inquiring minds want to know."
At least with a Canon DSLR, if I set the "Picture Style" to Monochrome (B/W), it will show b/w on the LCD screen. However, I'm 99.44% confident that the RAW file still has all the actual RGB bits. I didn't proceed to see what LR actually imports, however.