I built a pad for my pool since I built it on a low spot on my property and needed to get it higher than the creek right next to it since the creek sometimes crests the banks.
The pad is about 1.5-2 feet thick at it's highest location, it is made of whatever pile of dirt I had kicking around - probably clay since everything here is clay!
On top of that I used stone dust to complete levelling the pool - the pad wintered for one season before I started building, however I believe the same compaction could easily be achieve using the right equipment.
I really don't think you have anyhting to worry about.

Pool manufacturers highly warn against it since AG pools are generally designed with "self install" in mind, I believe the manufacturers want to avoid unnecessary attempted warranty claims because if Joe Spadeandrake were to do it, he likely won't compact it properly causing early structural failure.