As of Flux 8.1, File Actions and Triggers do not support Amazon S3.
Flux 8.2 will support Amazon S3 within all of Flux's File Actions and Triggers. It's as simple as selecting "S3 Host" from the list of sources and filling out the region, bucket, access ID, and secret access key information.
This feature is similar to Flux's support for UNC Host, FTP Host, FTP SSL Host, and Secure FTP Host.
Flux 8.2 is coming soon!