i dont think spanking is abuse, however what your husband did would be looked at more towards abuse. but a little spank here or there wont hurt.
it is a way of discipline, and sometimes when a child misbehaves endlessly like you described his sister, they need a little spank to get them to realize that what their doing is not acceptable, and they need to listen now.
but hitting in the head, grabbing and yanking them upstairs...that looks and sounds like abuse. there's no need for that.
my fiancee has a daughter who is 6years old now, and he has given her a spank once in a while, not extremely hard, and not in the face, she would get a spank on the bum, and he would explain why he did spank her and that was she was doing is not tolerated, and she needs to listen when he says to do something.
shes now 6years old, and because of that discipline [which again did not happen frequently] she is a great kid.
You can take her shopping and say 'no we are not here for toys, do not run around, ok we're leaving grandma's house, put your toys away please, go get ready for bed' and there's no fight, no need for a spank, because she knows that she is to do what she's been told to do, and shes the sweetest little girl ever. and has no trama like some say they get when spanked.
Spanking is not aways a bad thing, sometimes kids need it once in a while, but i think how your boyfriend handled things was wrong. that is abuse like you said, and no kid deserves that, no matter how bad they may be.
Maybe your husband thinks this is fine because of the fact that he was abused, and brought up in this way. Maybe you could take to someone like a counsellor with your husband about this.
To some it is abuse, but to others its not. but its all in how you handle the situation and how hard the spank is. I dont think a 7 year old deserves 30 spanks...