Keeping him as a stallion doesn't necessarily mean he was used for breeding. Some people (son in law is a prime example) just think owning a stallion is more macho than owning a gelding.
I agree that his conformation is pretty poor, and his leg problems are very distressing to see. However, he doesn't appear to be in a great deal of pain, and if something can be done to help correct the right leg - like the corrective shoeing you mentioned, he looks like he would be a good pasture pet, as Poco mentioned.
Our neighbor had a horse with a hock swelling very similar to the one this horse has. It was also due to a fracture that healed abnormally in spite of vet care. His horse wasn't as bad off as this one appears to be, but was very content as a pasture pet and occasional lead line horse for the little grandkids. The horse lived to be 37 years old, and in spite of the hitch in his gitalong, ran, bucked and played in the pasture until the day he died.
Plain Old Dee, horses Dancer and Rain I believe in dragons, unicorns, good men and other mythical creatures!