This was my first instinct as a self-employed person. ;-) I tried to find corroboration but haven't found anything directly on point. However, the English instructions from Skatteetaten at the link pose the question, "Are you an employee or self-employed/engaged in business?"

This suggests there's a distinction between "self-employed" and "engaged in a business". I think that distinction fits fairly well with the distinction in usage between "næringsutøvende" and "næringsdrivende" when you look at those who are typically "næringsutøvende" -- artisans, small scale loggers, fishers, and yes, perhaps translators as well.

I'd have more confidence in my suggestion if I could find an actual pairing. I won't be surprised to see my suggestion questioned, and I look forward to seeing any alternatives.