I think that was a claim made years back, but I don't believe Redline has ever actually publicly stated that their 5W-30 is VII-free. AMSOIL used to make a 10W-30/SAE30 oil that was, not sure if they do anymore.
You could absolutely make a VII-free lube using Group III, it's just not going to have a great Winter grade; or not as good as one using PAO, which has inherently better Winter grade performance.
20W would be a 20 Winter grade (which does exist as a monograde). 20 grade or xW-20 would be the correct way to reference the use of a 20 grade while remaining ambiguous on whatever the Winter grade it carries is.