It’s a pretty complex subject in real life. Moreso with an autistic child.
My oldest, now 10, would get frustrated and try to hit me. Each time I would stop her and teach to make a proper karate fist and throw a proper punch instead of a girly little punch. She quickly got tired of the karate lessons. She will, however, occasionally try to hit one of her twin sisters. That’s always a time out. And it’s been several times when I’ve physically intervened (pulled someone away).
The twins, now 6, is a LOT more complicated. Oldest twin has quite the temper. She’s punched both of her sisters and tried to punch me. She gets a timeout for any infraction. I also am working on her to “use words” instead of just grabbing or pushing. I find it amazing that kids tend to grab first and have a whole rationale behind the action, but don’t think of vocalizing it first.
Youngest twin is autistic. Timeouts have no meaning and are irrelevant. She has a very high pain threshhold. Also, getting spanked is something she tries to get as an attention seeking action. Or hell, I dunno, maybe she thinks it’s normal. Eg, throwing a cup of milk on the floor, and then asking or pantomiming to be spanked for doing that.
I had a 6 month period where she scratched. Badly. Drawing blood badly. I don’t know how many times I got my face ripped up but it was dozens. Of course, most of that was at night when she had horrendous sleep issues (now solved through very mild nighttime medication). it took about 6 months of me flicking my finger irritatingly hard on the back of her hand to cut it out. More like 2 years for her to stop doing this to the rest of the family including her mother.
This is not something that timeouts help with (she doesn’t understand the concept of timeouts) or a spanking helps with (it’s not a deterrent) or shame works with (she doesn’t understand language very well), and hitting her wouldn’t do anything but confuse her more. She did get spanked or hand slapped painfully hard a couple of times for attacking her twin. But it was not a cause and effect deterrent, and much more a horribly confused “what did I do wrong crying” that would break any parents heart.
Hell, her mother and I did the happy dance the first time the autistic twin pushed her twin off the kids love seat. It was a “normal” sibling physcial altercation. And the first normal one in 5 years. I certainly don’t want to see her smack her older sisters, but part of me will be overjoyed when she does at a justifiable time. Welcome to austism. 
Qin - your question has a lot more grey areas than you can probably imagine at this time.
And just to be clear - we don’t allow hitting in the family where at all possible.