Never found an answer for the missing button; however, a work around was to Add the administrator like normal, then click on the section heading in the left column for Administrator Account. That took me to the screen where I would add a non LDAP user manually as an admin. I just skipped that step and completed from there.
After that however, the page never loaded what to do to complete the install, it sat on a "loading" style page.
After an hour I came back and just closed that as it wasn't doing anything.
The server GUI launched fine. The admin panel no longer takes me to the setup page but to the server management page, which is good.
I manually installed Spark on a test terminal and (after manually adding 5222 to the server's firewall exception list) was able to successfully connect to the server.