>>45197529If anything that's the most damning evidence for Ghetsis being N's real father. You think Ghetsis was just a normal guy until one day he stumbled across a Tarzan kid and suddenly got a plan for world domination? It's much more likely he placed N in a carefully cultivated forest environment himself and introduced himself once N was old to have bonded with the Pokémon but young enough that he can teach him how to speak human language along with reading, writing and mathematics.
Remember that N grew up surrounded by abused Pokémon that Team Plasma had sent to him. He was shocked to discover the player's Pokémon actually like humans because it was the first time he had ever met any that weren't abused. By that fact we already know that N grew up in artificial circumstances for most of his life, it stands to reason he was raised in such a way since birth.
Of course that doesn't prove Ghetsis was his biological father either. For all we know the above could all be true but Ghetsis just kidnapped the infant N from someone else and then sent him to the woods.
To answer OP's question, I think that even if Game Freak intended for them to be unrelated, they gave them the same hair colour so it at least wouldn't give it away to new players at first glance.