Bitnami provides the VM with DreamFactory already configured and shipped with the rest of components that Dreamfactoy needs in order to work. For instance, Dreamfactory uses MariaDB and Apache, so bitnami packages Apache+MariaDB+Dreamfactory+other components in a single stack and then creates a VM that can be easily launched on AWS by publishing those VM in the AWS marketplace.
Bitnami just provide AMIs to the marketplace which are free of charge, secure, up-to-date, consistent and fully configured. In other words, Bitnami contributes to populate the AWS marketplace.
You can decide wether to use the AWS Cloud Storage server or a more complex solution such as Dreamfactory: