There is nothing guaranteed about it. There are many gulfstream grads throughout the industry and they all the say the same thing, not many people actually get "hired" to fly for GIA. Most just spend a lot of money there, get some right seat time in the B1900 and move on to bigger and better things. It certainly is a nice shortcut around more traditional career paths, but it is looked down on by many people in the Industry and I wouldn't recommend it. I have seen GIA grads working for all of the airlines I have worked for over the years, they get hired, but they also get a lot of grief from their peers. So that's a decision you have to make. Generally pilots look down on others trying to shortcut the normal progression, they feel you have to "Pay your dues" like they did. This means a different thing in this day and age though, airlines are currently hiring with as little as 250hrs and a cmel rating right into a Jet. You could have the same kind of fast progression these days by just going to a school like ALL ATPS (their grads are usually hired very quickly). Get some good training, get some multi engine time and move on.