I had my instrument already done. I took my commercial a week after I got to ATP and my CFI's a week after that. ATP has the Gleims test prep -- it's really helpful in studying. I spent my off time going over and over the test on the Gleims prep and scored a 92 on my commerical, 96 on my CFI and 100 on my FOI -- that's with no prep before getting to ATP. I know that anyone with a good work ethic and a decent brain can do just as well if not better than me if they set their mind to it. Also, ATP is going to send you 26 pounds of books before you start -- you bury your nose in those and do the Gleims prep on a regular basis and you'll do fine.
If you're asking about the published books that they send you -- it's ASA oral preps, PTS, Jepp Instrument/Commercial, Instrument Flying Handbook, Instructors Handbook, Turbine Handbook, Mutli Flying Handbook, Gleims written test preps -- pretty much every book that you'll need.
If you're asking about the Seminole supplement and checklists, I believe they're written by ATP's Chief Pilot, Rich Tillery.