Yes, it doesn't work with a SSL-enabled (it's SSL, or more precisely, TLS, not ssh) client (in your case curl) because of a self-signed cert. It's normal with Cloud trial instances. And your question is?
Non-trial Cloud service uses proper certificates issued by a well-known CA. Since trial is not meant to process any sensitive data Splunk uses self-signed certs. You can use SSL on those connections you just have to disable certificate verification on the sending side. (like curl with -k option does)
