I have a mare that broke her shoulder at 4 months old was put in a box stall that was 6 by 8 for 8 months, her shoulder healed fine but because of not being able to move around her other front leg has serious issues, she will never be sound to ride, but she is not in pain, and gets around just fine, she can run and play. When I got her, her knees were the size of cantaloupes and she could barely get around, I basically got her to put her down, but after a few weeks of good feeding and open spaces her knees went down and she could move more freely, she had to learn how to run again, and stop, she fell on her face several times learning to stop and turn. She shows no sign of any pain.
If he's been that way since birth is it possible that his hip dislocated during the birth process and maybe it can be popped back in? It's up to you if you want to try to help this horse or not, but go in with the mindset of yes there will be vet bills. Is this little guy happy and health besides his hip issue?