You can create accounts from your site using just about any language that knows how to use XML - check out the API documentation here.
As for interacting directly with the Iworx-DB - I don’t believe this is possible. Iworx uses it’s own copy of PHP and MySQL from what runs the sites created in it. Therefore, I don’t think you’d be able to connect to the Iworx-DB directly.
I’m sure an Iworx person will clarify. As for using a shell script, I suppose it would be possible. It’d be just a matter of writing the appropriate commands, but there’s a lot more involved in setting up subdomains and SSL certificates. Subdomains require additions to the Apache conf files, updates to the DNS server, etc. SSL Certs require files to be moved around and installed and Apache’s conf files to be updated.