Popular celebs have a lot of fans and it can influence them to play on the same platform their idol is playing, the marketing spend by casino is going to be worth it. They can recover it and make more than it.
That's the expectation why he becomes an ambassador of Stake, without good result, it's a dead investment on the part of stake.com. So, this automatically means that stake is going globally as they hire a popular artist worldwide and you know what influence can do.
They don't need to pay all of the world's celebrities to spread the word about stake casino. You see, celebrities have such a strong effect, fans are willing to do, say, or wear anything their favourite artists do, say, or wear. If you look at a celebrity's life, you'll see that the majority of the products they use are simply sponsors, they don't own them, they only use them to get their fans to use them as well. That's precisely what Drake is doing, and that is why the first game he played I never believed he actually did it for fun but for partnership between stake and Drake management.
On the other hand, I believe that Drake was an active player on stake already before stake noticed him as potential ambassador.
I think, he was already a big roller even before this collaboration. Though it doesn't matter now.
Stake got Drake on their camp, and as it shows right now, a lot are getting interested on stake because of him.
So yes, it seems that he will give good income to the casino for this partnership. Anyway, the casino is already one of the big ones in this industry.
Later on, we may see other casinos following their steps of hiring known celebrities or personalities to promote their site.