From experience, it’s unlikely to have any issues. I have a couple 9x boxes that I had to bring online awhile ago because I needed drivers and didn’t have a spare CD to burn to move them over, nor a functional new enough computer with a floppy disk drive (both issues I’ve fixed), and they were fine in the short bit I needed them to be. Even actively trying to get such a device infected, which I tried just for curiosity, is often a losing game, because you have to find ancient viruses that aren’t even in regular distribution anymore to cause a serious threat to it.

That being said, Windows XP appears to be counter-intuitively more vulnerable, because exploits for Windows NT-based systems are still targeted with XP on the list of targets, and especially since XP is more usually run in a VM, there are ways to infect a reasonably modern host system from there.