I guess you thinks that our S3 compatible gateway is using Amazon? Then answer is No. It still uses Storj DCS, just S3 protocol instead of native and all encryption is happening on S3 gateway, then pieces are distributed across the network as usual.
To use an S3 protocol you may generate S3 credentials in the satellite UI or with the uplink CLI or with bindings and use them to configure the S3 access in your application using AWS S3 SDK or any other S3-compatible SDK, just need to provide a generated Access Key, Secret Key and Endpoint. The Endpoint will tell the library, that it should contact our S3 gateway, not Amazon’s one.