My GUESS is that, no you wouldn't be able to use the Check Point API to access your S3 bucket from outside your AWS infrastructure. S3 is an Amazon thing, not a Check Point thing. S3 access from the outside is going to require IAMs and all that good stuff - it really is (as I understand it) designed for storage of assets for use by other AWS assets (EC2 instances, EBS setups, etc.) that then serve things out via web interfaces. It's easy enough to post to an S3 bucket with web code, but that's not the case with a Check Point box. It's not a web server
Surely, there is a way to skin this cat, but I don't think it's going to be Check Point API. You'll probably need to write a script using an AWS SDK that knows how to talk to the AWS API and such. If anybody knows how to do that on a Check Point box, I am all ears.