Yes, I have a friend that is flying for Chicago Express and has just been hired by ATA. He was a captain on the Saab for 2 years, and he is now in ATA's pool.
And you are wrong about training cost. If mainlines dont hire there wholly owns, they simply go somewhere else. So now u still have to train at the regional. And mainline still has to hire. If you have a flow, I think people will have a tendency to stay at that regional longer for a job at mainline. When mainline US Airways wasn't hiring our Piedmont guys, we still lost a ton to (at the time) United, American, Southwest etc..... And US Airways had to hire a bunch of people for the regionals. I personally think it save money to have a flow thru... just my opinion.