No, I was able to soft-reset for an Adamant natured Rayquaza. When I was soft-resetting, each Rayquaza would have different IVs, but all of them had three perfect IVs. It might be possible to get more than three, but like other events, you won't get less than three. I'm almost certain three is the only amount you can get, though.
As for Galileo, he was an astromoner and it could be related to how Rayquaza goes with you to space to defeat/capture Deoxys.