I know you weren't asking me, but I thought I'd share a publication by the University of Colorado specifically addressing the issue at hand.
http://cires.colorado.edu/limnology/pubs/pdfs/Pub079.pdf
It's my observation that the effects of salt on nitrite toxicity is unchallenged by the serious aquarist community.
Here is an excellent article by Matt Clarke on the use of salt in the aquarium. I strongly urge anyone who has any questions on the subject to read the article.
At the risk of sounding combative, I'll note this because OP and readers should understand it. As well meaning as Mr. Limpets comment on salts effects on nitrite toxicity was, in this case it simply wasn't rooted in fact.