As far as I know in the last few hiring cycles at Atlas they have used a pool. It is also my understanding that it is a competitive pool, meaning everyone is ranked in the pool and people can come into the pool at the top and get an almost immediate class date, and conversely one could be the low man on the totem pole and theoretically never get called.
Good luck to everyone at Atlas and to those trying to get on there, my impression during my interview was of a class organization.