A primary use case for us getting this tool is to move our DNS to a new provider. I was a little shocked that there is no way to ingest an existing DNS domain into this service natively.
BIND Zone file import & AFXR based creation should be standard.
I couldn't even find scripts to do this basic onboarding, so I wrote some.
The scripts require dnsPython. They're crude and unpolished, but at least I was able to use the product.
migrate-zone-primary.py does an AXFR based transfer migration to a Primary zone
parse-zonefile.py will parse all files in subdir 'zones' that end in .zf and create Primary zones based off them. i.e. (zones/mydomain.com.zf) Currently it uses the filename for the zone creation string, but I'd probably get smarter with that and use the SOA or something to pull the domain from the file.