
Lea, I personally haven't used Devils Claw in the treatment of arthritis in dogs but I do know of a bloke who has used it as an analgesic and anti-inflammatory in horses rather successfully. I would say it can be used in dogs too.
You asked if there was anything else that could be used in dogs to ease the joints. In addition to the above, there are....
Chondroprotecive supplements such as Glucosamine and Chronioitin, MSM.
Homeopathic remedies, acupuncture can help too, ultrasound, acupressure, there's loads.
Hydrotherapy is excellent for arthritis.
Magnetic Therapy (although Isabel doesn't agree) ;-)
There are lots of herbal treatments but it might be better going to a Homeopathic vet if you wish to explore this avenue to discuss which may be helpful to your dog.
Hope this gives you a few ideas.