I've come to the illumos ecosystem about three years ago. First for SmartOS and ZFS. Now i know more about the great tech if offers like zones, dtrace and so on and use it nearly on all our servers.
I know others are joining the community as well as hanging around on irc shows. It definitly is a smaller community than linux or the BSDs but it is growing.
Also a lot of interesting systems development is happening (lx-branded zones, overlay networking, ...) in illumos and it is the upstream of openzfs.
Besides SmartOS a more classical server distribution to consider would be OmniOS [1]. For a storage appliance one might want nexentastor.
Distributions of illumos are more purpose-built than linux distributions. They differentiate more by use-case than by package management. Yet they all consume and contribute to illumos and what might look fragemented is not much of an issue for the community itself.