It depends on a lot of things.
First, most of the ones born in Nigeria will do it for a green card. So be careful. They "fake marry" Nigerian women for green cards too.
Second, I'll use my dad and other male relatives as an example. My dad went to college here (California) then moved back to Nigeria. He said when he was here he only dated Black American women, but never had any intention of marrying one, mostly because my grandparents warned him that they wouldn't go for it. After school, he went back to Nigeria and married there, then came back here. All of his friends did the same, as did all my male cousins who schooled here and England. It is the norm, but there are small exceptions to the rule.
Third, its not just about you and him. Its about his family too. I've never seen Nigerian's family happy to hear that their child is marrying a non-Nigerian. Most of the men are very close to their families so even if he likes you, marrying into a family that is cold and distant towards you isn't fun.
Going along with that, I've seen with cousins and family friends how they marry Black American women and not only do their families reject them, but its clear on holiday functions and family events that they favor the grandchildren of the Nigerian daughter-in-law. It can be awkward. Most Nigerian men will not stand up to their families in support of their wife. The way the culture works is that the wife does more of the compromising in that respect. My cousin married a black American lady and my uncle and his wife barely speak to her. They always tell my cousin to come back home and get a "real wife."
It can work, but from the perspective of an actual Nigerian, I wouldn't want my daughter or someone I care about to do it. I've even seen families not come to weddings or refuse to admit to their friends and family that their son has gotten married to a non-Nigerian.
If his parents are dead or divorced, then disregard everything I said. Lack of family structure overrides all of this. Its an intact family to effectively reject a man.
Also, don't be fooled if a Nigerian guy introduces his parents to you and they are nice. It doesn't mean they are accepting. As soon as you leave, they may sit him down and lecture him for 2 hours on why marrying you is a terrible idea. Sometimes its a tactic to make the woman feel comfortable so she doesn't feel threatened, so they can use that time to plant seeds of doubt in the son so it comes across as though he ended the relationship out of his own free will.
Oh and none of this is because Nigerians don't like Black Americans. The same thing goes for Caribbeans, and people from other African countries. Nigerians are tribalisitic, once their child marries out of their tribe, its basically like marrying another race or nationality.
I can also add, my parents have told us all bluntly that they do not want non-Nigerian in-laws as have the parents of all my American-born Nigerian friends. Him being American raised doesn't make a huge difference, although if he was born here the whole, pleasing his parents thing may or may not be lessened, that depends on the individual.