As far as I know, Blizzard doesn't pay streamers under the table to play and praise their games, this specific thing was just for the sake of the joke.

This said, there is this rumor the numbers of the Overwatch League are inflated, either by embedding the stream on multiple platforms, viewbots or simply but giving people rewards to "watch" the stream. I say "watch" because lots of people just let it play in the background while they do whatever. What this means is there are not many eyeballs following it and it's perhaps not as succesful as it was supposed to be.

Of course, this may be all a rumor, Overwatch League may be growing steadily and overtake Fortnite and even Soccer has the thing to watch in the future.

The truth is, it's pretty hard to know the real numbers however I don't meet many people who are interested on it but this is just my personal experience. Your corner of the world may be full of people wearing OWL jerseys discussing yesterday games.

But somehow I have my doubts about it.