Q1: Yes, this will be shown in the customers account for the customer's part of the cost. SaaS provider will also see their own part of the cost. Both parties will have some IN and OUT traffic.
If the VPCs in the VPC peering connection are within the same region, the charges for transferring data within the VPC peering connection are the same as the charges for transferring data across Availability Zones. If the VPCs are in different AWS Regions, inter-region data transfer costs apply.
Data transferred "in" to and "out" from Amazon EC2, Amazon RDS, Amazon Redshift , Amazon DynamoDB Accelerator (DAX), and Amazon ElastiCache instances or Elastic Network Interfaces across Availability Zones or VPC Peering connections in the same AWS Region is charged at $0.01/GB in each direction.
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