I don't even understand why there's anything to discuss.
It's obvious that for a low-maintenance server, you want a distribution that provides security bugfixes for as long as possible, so you have to do a major manual upgrade as infrequently as possible. Fedora does not provide such a stream of fixes. So Fedora is not the right tool for this job.
RHEL would be the obvious choice, if Red Hat gave the Fedora project free licenses, and if the sysadmin were most familiar with Fedora or RHEL. Centos is almost the same, with no licenses needed.
But if the person doing the sysadmin (especially on a volunteer basis?) is most familiar with Ubuntu, then that makes Ubuntu the obvious choice in that location. Force a volunteer off his area of expertise, and at best he makes more mistakes, and/or accomplishes less in his limited amount of time. At worst, he stops volunteering!