Nighthawk does have a Superpower, and it's what makes him The Determinator.
In Supreme Power: Nighthawk, Whiteface remarks that Nighthawk was poisoned with enough of his toxin to kill him, but it just made him cough blood and pass out for a while.What if the retrovirus gave him The Power of Hate that allows him to push past and go beyond what a regular human is expected to survive?
Similar to the "invisible mutation" that Emil received that any outside person would simply write off as the efforts of an exceptional individual, rather than the result of genetic engineering.
It would explain why he's such a hateful person in general, and it would be a nice dig at Batman's own status as the Charles Atlas Superpower poster-boy — the reason why he has such inhuman will is because he isn't human.
