I have never flown any ATP planes or been affiliated with the school, but I've talked to instructors there a decent amount.
They get paid on salary, $1,500 a month or $2,000 a month if your considered the supervisor. They work 7 days a week... and thats from fairly early in the morning until its dark out and time to go home to sleep. They push their students in and out so quickly I wonder i the students really have enough time to absorb and feel comfortable with all the information they're being taught.
So basically, the salary guarentees them a paycheck. Not many places can say that. If you do the math for how often they are there (from the time they walk in until the time they leave) the pay comes out to like $3 an hour, but $1,500 is probably still more than alot of CFIs make in a month.
They seem to have a steady flow of students and get a decent amount of experience.
You wear uniforms and have official looking airplanes so I guess it feels like more of a real job than most CFI gigs.