Depends why the horse had the splint! If it was due to hideous conformation.... No!
There are lots of reasons for splints... they are sometimes caused by nothing more than a knock in the field.
They do not normaly affect soundness unless it is right near the knee. They might be a deciding factor in the show ring... ie, If I had to choose between two equaly good horses, one with a splint and one without I would choose the one without!
Ehm, no, but purely cos I think there are plenty of horses out there without problems..... and remember it would be a pre-existing condition and therefore not insurable.
Never known a horse not to have one or two, or one developing. Its a strengthening process that bonds the splint bone to the cannon bone with newly laid down bone. Usually starts as a young horse start taking on more concussive work. The inflammatory process that initiates the bone growth can be painful and cause lameness, but it soon passes and its never been a problem to me or anyone I've known with horses.