we need to remember that oscars ceremonies have become 'roasts' over the years. A clearly defined and expected situation where a clebrity will be the target of insults and mockery, along with fellow attendees. Everybody knows this. It's got a little of the flavour of court jestering, and takes into account that everyone there has high social capitol.
So it's a defined space where people get mocked and are supposed to take it. Outside of the ceremony, one wouldn't expect them to take it.
I think Chris Rock is a knob for his trans stance but here, compared with Gervais, his roasting is tame