When you get a % of losses, they will try to argue that you are, in fact, acting as a casino.
This would be difficult to prove for them also, but they would try.
The less avenues you give them to pursue, the better.
The wagering % as used by Casino Rewards and Fortune is also a way that you are not sharing the profits/losses directly, as is the % of deposit Slotland offers.
Obviously I am not a lawyer and these comments are not to be construed as legal advice but are solely for your entertainment.