No doubt you are thinking of the fact that RA is caused by an antibody reaction whereby the body's own immune system gets skewed and starts attacking it's own tissues? Well, no it won't fight the implants as the implants are not only foreign bodies but inert as well and the immune system won't 'see' them at all. They'll be under the radar, so to speak.
However, flare ups can still be a problem in other joints (of course). But in the knee, they should be minimal as nearly all the synovial membrane and articular cartilage will have been removed.