I would say that those who have a long track-record and advertise on the forum are safe, such as Bitvest.io. But there are others as well. I don't think any are significantly safer than the others.
I agree, there aren't 'safer' casinos to invest in but doing due diligence can help. This is why track-record and reading reviews would give you a better idea of which places might enable you to minimize your risk. I too stand by Bitvest.io - it has been around long enough to know that you won't get scammed.