"Is it possible to create a forensic image from an AWS Elastic Block Storage (EBS) snapshot and process it in Forensic Tools?"
No. Because of limitations imposed by AWS, you must "rehydrate" or restore the snapshot image from a snapshot to an EBS volume. You must then attach that volume to an EC2 Instance and use FTK to acquire your forensic image.
"Can we create a forensic image from an AWS Relational Database Service (RDS) snapshot and process it in Forensic Too?
Because of how RDS snapshots are stored, we are unable to process them as block storage and image them, and you would have to dump the database to an EBS volume, attach it to an Elastic Compute Cloud (EC2) instance, and then perform your forensic image acquisition.
Link: Amazon EBS Snapshots