Most webservers run Ubuntu and it is the default OS for the overwhelming amount of cloud providers. Some run Debian though. Most enterprise applications run Red Hat or CentOS.
I never heard of OmniOS. Quick search says it is a distant descendant of OpenSolaris.
Given how rare that was already used back in its time and how practically nullexistent the community is for it (compared to Linux) I can say with high confidence the users are limited to a few enthusiasts and hobbyists.
Alpine is a special case and is indeed quite useful on VMs or IoT devices. I used it successful as base for a taped-together home automation server on a repurposed android phone.
I would also have a look at the XDA forum. A very large percentage of devices that are not officially supported have unofficial ports (Lineage and others) that run 99% as well as the official ones.
e.g. my old Galaxy S8 was not official supported but one of the staff members of XDA made a port that runs like an absolute dream.