Considering you pay the type rating provider direct (same cost as other airlines/students)I fail to see how RYR make a cent out of it.
I think it's more the fact that while you're line training, you are free to them. So they make more money having newly rated pilots flying than they do their experienced FOs. So technically it is good from a business point of view to keep hiring FOs because they are costing nothing and giving you less cost on all the flights they operate on.