I don't see why not. Replication is just a command stream over a network. You can secure it over the daabsse's built in TLS support or over VPN. The only question is bandwidth and latency between your DC and AWS's.
You don't need to get the RDS box on a VPN. Instead, you get your server in your data center into the AWS VPC via the AWS Gateway VPN thing. From there you tell your data center server that it's master is the RDS box and you should be all good (assuming you can do the usual song and dance with the full DB dump and replication coordinates).