Jim, Welcome to LR Forums.
I believe you will find that it's the on-board graphic adapter solutions that are using system ram. Look at a Dell ad, and you'll usually find an asterisk footnote about 'shared' memory, system vs graphics. (There must have been a class action suit from people who felt they were stiffed on their RAM).
Low end graphic adapters fundamentally provide memory to hold the pixel map of what your screen is to look like, and the electronic circuitry to convert that to the video signal that your monitor is expecting to see.
Higher end GPU solutions provide more memory to (more or less) hold more than one screen at a time so that screen animation is faster. In high frame rate motion graphics, i.e. games, the moving 3-D objects are rendered on the fly. This means that the images are not processed as pixels, so much as they are geometric data descriptions of the objects that are turned into pixels via mathematical calculations. The more GPU power, the simpler/faster the instruction stream can be to the external Graphics pipeline, thus lowering the load on the system memory and processor.
So, no, a good graphics card actually 'unburdens' the CPU system memory. Although there are probably tuning/compatability issues involved in any specific combination.
In the instance of LR2, there 'seems' to be an issue with a specific generation(s) of adapters from a specific manufacturer, which 'seems' to be having a huge negative impact on performance, which again 'seems' to be specific to some of the 'optimized' hardware rendering of 3D aspects of the images. Since there really are no 3D acceleration aspects to LR rendering, this is counterintuitve. But the problem seems to be quite real. I believe engineers from the two companies are investigating.
At this point, I wouldn't abandon my GPU for the motherboard adaptor. But at the same time, if you're suffering performance issues, it might not be a waste of time to give it a try and empirically test the results. As I said, there are some goofy things going on with LR in this area, which have not yet been completely characterized.