I don't think the error you are seeing is related to your air-gapped environment. We support that via the image attribute. See Discussion of custom images
The error you are seeing is caused by the webhook service that we deploy not being available. We have seen the same error in our e2e test suite and are looking into that.
If you have any logs to share that could be helpful in narrowing down what is causing this issue.
The operator logs can be retrieved with
kubectl -n elastic-system logs -f statefulset.apps/elastic-operator