The airlines look at WHERE you did your flight training. They also look at a first time pass in the IR. The school is very important, it is a stepping stone to your future. That said, there are many airlines hiring outside the big schools but the pass rate is also there after.
Re.: The ATPLs: You are only required to pass. You grades are not that important, they will not be shown to your employer during the interview. However on a personal note: lower grades normally indicate that you might have problems down the road - Like passing a TR + Tech and getting through LT without any hiccups.
If you were on the other side of the table WHO would you hire???
***A nice guy, with reasonable knowledge, good hand eye coordination (good flying skills), a person that is ready to take on the challenges and the responsibility with his/her new job.
All the best.