S.M.
I would have to say that after growing up with a father who was passive-aggressive, I think that your son will make his own decision about his father eventually. Yes, it hurts when a parent doesn't approve because no matter how old we are, we want our parents' approval.
That said, it sounds like you've raised an amazing young man (and there should be more like him in this world)...encourage him to follow his dream. If he ends up doing something he loves, it will show in the way he lives his life and treats others. To take on a profession to make someone else happy or to accept you will just make the light he is diminish and he would end up bitter and an unhappy mess.
It is sad that your husband cannot see who your son is and what potential his son has. It's sad that he cannot see beyond HIS wants and desires. What does he do for a living? Is he happy at it? Or is it a case of "misery loves company"?
I would say just talk with your son, explain that his dad loves him, but just wants different things and doesn't understand...he will someday or he won't but that shouldn't color your son's dreams. Don't say negative things about his dad, let him love you for letting him see his dad in his own light not yours (my mother did this for my brother and I and we know our dad loves us, he's just miserable and can't move beyond it himself)...just keep encouraging your son to do what he thinks is best for him and will make him happy.
As far as your ex refusing to pay for application fees, etc. I find that those things manage to work themselves out when it's right. Your ex will either come around, or your son will find a scholarship or other funding to help pay for the necessary things.
Good luck. and thanks for telling us that there is a wonderful young man about to enter our "adult world".