The BSDs aren't distros, though some do have what might be called distros, such as PC BSD, pfSense, &c. being distros of FreeBSD, EdgeBSD being a distro of NetBSD.

The ports system is a rolling release system for non-base software though, though the base OS isn't. The closest BSD to come to having a rolling release schedule for the base OS is OpenBSD, with its six-month release cycle. The thing is that the BSDs can't have a rolling release schedule as is found in some Linux distros because the base OS is managed separately from the ports/packages: the core OS components aren't packaged, so there's no sense in which they can 'roll'.

Personally, I'd never use an OS with a rolling release cycle on a server. Too much can go wrong.