Conditioning is one of the best ways to keep your horse sound for life, regardless of what kind of riding you do. Conformation plays a big part, too.
When you condition your horse correctly and you know how to ride, you're significantly decreasing the chance of injury, just like with any athlete. My trainer did hunter/jumpers, showjumping, and reining with her old horse, right up until she lost him to colic at age 29.
When a horse is physically fit to jump, I don't think it poses any more risk than galloping around the pasture like a maniac (like many of them do, especially in the spring