If so, how do you ask?
If you ask and they don't divulge, what do you do?
Unless you propose something where you take nothing upfront and then it comes from the revenue. But then again its about where the risk is, so if they have virtually guaranteed revenue then there is no risk taken and hence no reason to share the upside.
In short: More risk = More upside, otherwise the salary/fee is capped.
what the employees say in smalltalk is also useful. But the best hint are the contract negotiations.