It depends the circumstances. Was is actual domestic violence? Or was it two men drunk, going at it?
A woman is physically smaller and less muscular then a man. We don’t run races in the same category, we don’t pro wrestle in the same category. For a reason. It’s like a teenager bullying an eight year old. They’re just physically not as capable.
If it was him abusing his SO, then no it’s not okay, man or woman. If it was equal parts then whatever, hit away. But I absolutely hate it when people say it’s okay to hit a woman if she hits you. Are you kidding? Firstly, you don’t fight violence with violence. Lets use the eight year old versus seventeen year old analogy again. You pull the twat off you and don’t hurt them unless you’re defending yourself. If a woman could do that physically to a man, I would encourage the same.