Within specific limitations - both you and the tech type are correct - and in fact the answer you get may depend on the question you ask, how it's worded, and how it's interpreted.
If what you want to do is share the USB port (as a USB port) across the network, it can only be done using Shareport - however - when the DNS-323 debuted, it (and by the way, that was a number of years before Shareport), it offered, not a shared USB port, but a USB print server, and USB support for UPS systems (Uninterruptible Power Supply) was subsequently added.
I have used the USB port as a print server, without Shareport, and also used it with Shareport.