From what I can glean from the documentation on bitsavers, this is a multi-user system built from multiple CPUs (mostly Z80) running in cooperation. Each workstation seems to have it's own Z80, 64K, etc. I didn't see mention of an OS, but would guess it is a proprietary Wang product. Certainly not DOS and almost-certainly not Unix. Probably not CP/M-80, either. These are essentially multiple Z80-based computers in the same cabinet, that share common I/O resources (floppy, winchester, etc), with the I/O controllers also containing Z80s to offload from the workstation units. There appears to be DMA for exchanging data between workstations and I/O controllers, and perhaps some shared-memory (probably for command/response handling). A lot of (educated) guessing, but this does not look like something you can insert an MS-DOS floppy into and boot. Without the original Wang disks, the best you could do is write an OS from scratch that is only similar to the original. Depends on the ROMs, though... if they contain the "OS" then a recovered machine might be usable.
The BNCs carried serial data and connected to Wang servers, if memory serves. I believe that the DB25s were intended for printers, but it has been a long time since I read about this stuff.
Wang OIS was pretty involved and dovetailed with Wang VS. A good discussion is here: