Same scenario and same problem. I was able to fix it by adding this to the setDomainEnv.cmd script:
On the next startup of the managed server the output changed from
Using the default WebLogic SSL Hostname Verifier implementation
Using the configured custom SSL Hostname Verifier implementation: weblogic.security.utils.SSLWLSWildcardHostnameVerifier.
Before the change I had this problem as well:
<BEA-141151> <The Administration Server could not be reached at https://xxx:9501.>
<BEA-150018> <This server is being started in Managed Server independence mode in the absence of the Administration Server.>
I hope this will help someone, most topics and official support notes I have found on this just talk about disabling the hostname verification.