Workstation rather than server, this is basically a normal BabyAT board with (limited) onboard I/O that could even be stuck into a generic cramped minitower case. A server-oriented board would probably have EISA instead of ISA, probably no onboard I/O and might well be larger to accommodate more RAM.
As for "rare" - any dual So5 board is uncommon, I'd say this is one of the more frequently seen, well-documented and liked boards.
Bear in mind that in 1994-1995 the number of operating systems that could actually sensibly use SMP was very limited - so the use cases for a system like this were similarly limited. Basically this would have been used for a Windows NT 3.5 workstation, probably for CAD/CAM applications. And before you ask, it's pointless for gaming, no games that would run on an So5 CPU use SMP. It would have had 'snappier' general desktop performance than a single So5 board (in NT 3.5 or similar SMP OS), but that alone would never have justified the very significant added price of this SMP board and the second CPU.