In my opinion, workers can organize and demand higher pay if they want to, and employers can fire them if they know they can hire replacements of equal or higher value. The value of labor is subject to supply and demand just like every other commodity. So workers had better carefully gauge the market before threatening to quit. When we hire work done, we get a bid on the work, and if it's reasonable we hire it done, if not, we shop. As for the potential profit in the venture, the entity taking the risk makes the money. If voice actors feel like their work is integral to the project to the point that they deserve more money if it succeeds and are willing to stake their current time investment against their confidence in the value of their work, this is called "working for a percentage" and it's quite popular here.