I would say that about 80 percent of toyota cup players will play NRL at some stage of their career and about 50-60% will make a good living from the game.
This is looking a few years into the future, at the moment the competition is in the early days so most current NRL players didnt graduate but in the future almost all players will go through the Toyota cup, the exception being teenage prodigies who go straight to NRL, late bloomers and code switchers.
A lot of these players dont get signed up for first grade immediately after, there is only room for 5 or so in each clubs squad for the new season, many of them get their first grade shot when they hit their peak a few years later if they stick with it.
This is one of the problems for the NRL though, NRL clubs cant sign all the players up immediately so union can also take on outcasts they are impressed with. The Kennedy twins, John and Maurice who played at 6 and 7 and captained the strong dragons toyota cup team last year are an example of this. They didnt get a first grade contract for this season so they were signed by the Warringah rats union team, though they may be good enough for the NRL in a few years time, in a few years they could end up playing for the Waratahs instead