Well, usually the airlines don't care much about at which flight school you've received your training at, as long as you are a qualified pilot with a clean record (no accidents). And on the other hand having 1500 hr and the ATP under your belt, won't grantee you an airline job. I've the impression that you are a bit confused about that "must have 1500 hr" and ATP in order to get into an airline. Basically all you need to get hired as an FO (co-pilot) is a CPL+IR, that's it!
Regarding your initial question, building time as a CFI (certified flight instructor) in the US, that's part of the advertisement of most of the international flight schools in the US.
These schools promise a lot to get your money, but there are several factors which one must consider. First off, do you really get a job as an instructor after finishing training, because in the end it's the decision of the flight school. This mainly depends on how you conducted yourself during training, was there always a positive balance on your student account, were you a nice student or did you complain a lot, were there any incidents/accidents (that's pretty much the worst that could happen, especially an accident, could mark an early end to one's career).
Another factor which must be taken into account is, how much time will be left on your visa once you finished the training and will it be possible to reach the 1500 hrs required for the ATP in the time remaining. Common problem in this regard, as an instructor on visa, is to meet the 500 hr cross country time requirement for the ATP.
Another important question, how will the student supply be, if you wont have enough students it's pretty much impossible to reach the 1500 hr in the time remaining on the visa. From my own experience, I've been working as an instructor for a big international flight school in the US myself, I can tell you that usually it doesn't work to reach the ATP requirements, mainly due to the 500 hr cross-country time, which you don't get that much as CFI.
This "come to our flight school" do your training with us and work as an instructor afterwards and built valuable flight time which will get you into an airline cockpit sooner, it's only a bait to keep the money coming into the pocket of the school's owner.
Last edited by Transsonic2000; 29th June 2013 at 20:09.