Lightroom uses the same RAW processing pipeline as ACR. The tools are pretty much identical, though the UI is different. And, yes, I use CS6 in conjunction w/ LR4.x. It is necessary for pixel level editing, layers, masking, HDR 32 bit conversion, pano stitching, etc. My workflow is 80% LR, 20% CS6. Round-tripping from LR to CS6 is seamless & simple. An advantage of LR is that all of the processing is parametric, i.e. not cooked in.
I can recommend Jeff Schewe's book, "The Digital Negative," for a good treatise of the value of a CS6 / LR combination.