It's true he only sees his child as an experiment, but he does see him as his greatest experiment. He even acknowledges that Sephiroth is more powerful than science. The son has outstripped the father.
It's true that he did experiment on Sephiroth - but nowadays lots of parents tamper with their kids in the womb in order to give them a better chance in life. Sephiroth never seemed to dislike being a SOLDIER.
It's also true that he denied him any contact with his mother, but then again his mother is equally guilty of experimenting on her son in the womb plus she's seriously depressive, suicidal, froze herself inside a giant crystal, and thinks filling people up with monstrous summons materia is better than letting them die a natural death, so maybe it was in Sephiroth's best interests. I'm partly joking, but many parents have lied to their children about serious issues with the very best of intentions. Hojo isn't exactly good when it comes to dealing with emotions. Maybe he felt it would be easier on Sephiroth if he thought his mother was dead. Do you honestly think Lucretia would have made a good mother?
Every child is an experiment as far as its parents are concerned. Sephiroth's relationship with Hojo is like a metaphor for this. And a child's successes are always, in some sense, its parents' successes too. At the end, Hojo was willing to sacrifice everything for his son.
So basically what I'm saying is, there's plenty of room to interpret their relationship as abusive, but we can't say that it definitively was abusive. The only person who could decide that would be Sephiroth.