I don't think that the streams are scripted and I have no problem to watch streams of sponsored players if they announce in the beginning of the video that they are getting sponsored. It is more shady if they don't mention it but when you research it and find out that they are also sponsored, than it all stops for me.
It could be scripted. After all, we will never know and just enjoy the spectacle from the streamers. And if I watch the video from that streamer, I feel a bit jealous of them for being able to win the game with an amount I could never have imagined. But then again, I'm just a small player who can only dream that one day I can win a big amount, even though it's not as big as the streamers.
I do not think that it is scripted, but I am pretty sure that they are not playing with their own money. That's the only difference, casinos probably credit their accounts with some money and they tell them to play with it, and if they ever lose it all, that's the stream basically over, and for the next stream they credit some more.
This is why I believe that we are not seeing too many streamers really caring about losing too much, they literally end up losing millions and move on in some cases. When they win they probably get the money, don't know how that works if the money was given to them for free, but maybe that's their payment or something like that?