The streamer you were talking about used his own money under his own accord, the gambling casinos that he is playing in did not beg him to play with them so I don't see the reason for his complaints. These paid streamers get paid because there is risk in streaming casino games in their channel. Imagine a big streamer, known for solely playing League of Legends one day starting to stream casino games either full time or on the side, there's a huge possibility of him/her losing viewership which could cause loss of profit, so the payment these casinos give as sponsorship is a fair compensation for when that event happens.
I think that most streamers are getting no real bonus against the house. While their money is coming from the casinos, they are still playing the same games the average gambler is playing. The only difference is that the losses are not hurting the streamer. It is much easier to gamble if it is not your own money you are losing. In the end the streamer provides advertising which means more gamblers will join the game and increase the jackpot.
This too, I noticed some streamers winning way above average but most of them lose just as much as a regular player who doesn't stream would. That being said, in-house losses are the only thing that the streamer is shielded from, viewership and donations may also be affected because why would I watch someone play poker when I can switch to someone else who I know plays videogames at the same instance?
