The answer, IMO, is both. There are people who are naturally gifted, and who just have this ability to put the ball in the basket. Their mechanics may not be sound (see Jamaal Wilkes), but doggone it, they can shoot. And they have always been able to shoot.
But then you look at Ray Allen, who looks like the most naturally gifted shooter you can imagine, and he shoots hundreds, if not thousands, of times a day in practice. It's constant work. And I have personally seen players improve their shooting with proper coaching and better technique.
There are some players, however, who don't have the gift and there are others who simply cannot ever seem to learn or develop. They don't have touch, and for some reason they can't ever get touch.
So long story short, I don't think you can ever really predict with a high degree of confidence who will improve and who will not. Generally, I'm of the belief that the harder elite athletes work, with proper coaching, on skills, the better they will become at those skills. If Smart really wants to improve as a shooter, the more time he spends refining his shooting stroke and developing the muscle memory that is needed come game-time, then yes, he will likely become a better shooter.
All that said, clearly people cannot always be improving. Otherwise people would shoot 100%. Every person has an athletic ceiling, and for every person, that ceiling is different. I can work like crazy to improve my vertical, but I will never get to the point where I am jumping higher than Nate Robinson. It just will not ever happen. Similarly, it's possible that Smart will never become better than a 45% shooter. Maybe that's his ceiling. Who knows?
