Yes, SSB was the recommended way to update emunand to 8.1 when gateway didn't support 9.x at all. The 9.2 rom of SSB should work as well. But you have to be certain that you've formatted emunand before attempting to update it. If you're using sysnand in gateway mode updating from a rom will brick.
Thanks. I'm setting this up for someone else right now, so I wanted to be sure. I'm formatting EmuNand now, so no worries.
Edit: Maybe I'm doing something wrong. I'm on EmuNand 4.2, and when I attempt to run a game that I want to update with, it doesn't ask me for the update. It instead tries to play it. Am I missing something?