That's a good rake back, it's rare to find gambling site that offers 30% rake back. I would like to ask what games is this effective? All games or just certain games, does this include sports betting too? if yes then I would definitely enjoy this limited promotion.
I would guess that there are a few that does these type of promotions, not really common anywhere because it would basically make it near impossible for casinos to make a profit in the long term, but if it is just for promotion then they will have plenty that will lose, and some that will win and hope that it would equalize each other and if not then they would be paying just a bit more and they would consider that as marketing expense.
To do this long term would be the real challenge, just doing it for one week is not really that impossible to achieve, sure it "may" cost them some but they would not really be doing it as a pure loss or for your own good, they are doing it for marketing.