@Gabriel It looks like that is correct.
I spun up a server instance on my local mac, and the only way to connect a standalone instance of Bitbucket would be as an RWS and build out your own swagger definition since the API endpoints are completely different between any of the Bitbucket.org accounts and the Bitbucket Server accounts. You can still access BitBucket Server as you would any other HTTP service, you just do not get any swagger docs to go with.
BitBucket Server API reference:
https://docs.atlassian.com/bitbucket-server/rest/4.11.1/bitbucket-rest.html
BitBucket Server example:
Pass your basic auth creds in the cURL options using the PHP cURL option CURLOPT_USERPWD which allows you to send the basic auth credentials as {username}:{password}
Using test_rest to get a result back:
Or Postman:
I will put in a feature request to see about getting support added for the standalone server instances.