Well, I unfortunately know quite a bit about it. I was diagnosed 4 years ago. But I've never heard of it in dogs.
I don't know how they would treat it - it's an autoimmune disorder. Basically, your immune system interprets normal parts of your body as threats, and tries to destroy them, particularly with the synovial fluid in the joints. The "arthritis" part is largely a misnomer - while it does most commonly affect joints, it does not affect them in the same way as osteo (or "old people's") arthritis does. Osteo arthritis does not involve so much of an inflammatory reaction. Rheumatoid Autoimmune Disorder is a more descriptive term. It is related to other autoimmune diseases like Lupus, Sjogren's Syndrome, and Reynaud's Disease. In people, those with a diagnosis of any one of these runs a high risk of eventually developing a second autoimmune disease.
Left untreated, RA can spread to the heart, lungs, and kidneys - though no organ or system is exempt. Symptoms and their severity can vary greatly from patient to patient.
The first approach to treatment (in humans) involves NSAIDS like aspirin, tylenol, and naproxyn. But these only treat the symptoms, not the progression of the disease. Secondly, there are DMARDs - disease modifying anti-rheumatic drugs. The most commonly prescribed of these are methotrexate, which is a chemotherapy drug. These types of drugs lower the immune system's response and make the patient a bit more subject to catching whatever bug is going around. (I am on this, and during cold/flu season, I wear a surgical mask whenever I get out in public.) The third type of drug therapy is the Biologics - mostly in injectable form. These are drugs like Enbrel, Orencia, and tons of others. They are extremely expensive.
Some rheumatologists also prescribe steroids (like medrol or prednisone) to try and counteract the inflammation response. Another drug that is a first-line defense is Plaquenil, an anti-malarial drug.
The pain that goes along with RA can be almost unnoticeable some days, and be in a raging flare the next. No amount of exercise can prevent or lessen the pain - but it can help the initial morning stiffness to an extent. Stretching exercises are commonly recommended. It is concluded in some studies that exercising while a joint is inflamed is dangerous and causes more harm than good.
I am so sorry that your pup has this diagnosis. It is a difficult disease to live with, but not entirely unmanageable. It's not common to go into remission for several years, but it can and does happen. I can't imaging watching my dog go through this - I have enough trouble understanding it myself.