Hi James,
Thanks for your input.
I bought the domain directly on Amazon, so it shows up in Route53 under "Registered domains".
I am not sure if there is an API to update the nameservers that my domain is on. Keep in mind, these are two steps in Amazon:
1) Ensure the nameservers accept queries about your domain 2) Expose SOA and NS records in the hosted zone.
Step 2 is doable with Terraform, step one isn't yet.