if they don't have access, updating the roles won't actually change anything

Ahhh, That's good to know... I was just dealing with this the other day. I had no idea the CSV import results would show 'successful' even if they dont have access.. how does this make sense?!

It doesn't really. But in Netsuite's mind, I think the reasoning is: there's no specific error (you didn't do anything that wasn't allowed). It just fails silently because while the roles didn't get saved to the record, you didn't necessarily import them incorrectly.