Correct. SCSI would have been for if you wanted to use peripherals directly on a IIgs. As far as I know, there was never any server software for IIgs, that was always done on Macs or with other purpose-built hardware.
There’s a *lot* of them on eBay from China (If I remember correctly) so it kinda looked as if they were still being made, but maybe not.
I just searched on eBay and got thirteen hits.
The only brand name I don't recognize from around 1999-2004 is Ratoc. I looked at their web site and they appear not to be building a SCSI to Firewire or USB adapter at the moment, so I imagine what happened is Ratoc picked up the slack on these adapters a few years after OrangeMicro (belkin) and Iomega gave up on those adapters, and then stopped probably just a few years later.
My guess is either the same 13 items are just sitting there and the demand isn't actually that great, or this market is a lot like the market for DEC/Compaq/HP Alpha-based workstations and servers (especially anything that can run VMS): Not great, but extremely urgent and not particular cost-sensitive when it comes up (which means that machines around equivalent to your every-day G4 go for between one and three thousand dollars.)
One of the adapters mentioned a particular scanner. If that's a crazy high end drum scanner or something of the like, some shops are going to find more economy or utility in buying a $400 adapter to use with a modern (or even "modern") computer than bothering to mess with 20+ year-old computers and the attendant hassle of getting (legal) software and then, further, file transfer.
Relative to our position (here on the forum) where we already have most or all of the needed bits and processes down.