Rule 7.3.5 in the PBA rule book says that amateurs are not eligible to win exemptions. It wouldn't be right for it to go to the high PBA finisher you want to give a 2-year exemption to someone who didn't win?
If an amateur wins any PBA tournament, whether it's an open field tournament like the US Open or Masters or a exempt tournament, there's simply no exemption awarded for that tournament.
SH