Part, but not all, of the additive package can certainly be judged by the VOAs. Why do you think the calcium, magnesium, phosphorus, etc are all listed for? Certainly not all the ingredients are there; some of the proprietary stuff for the anti-agglomerates and detergents and such may not direction show up on a VOA, but at least some elements do!
To the real point, though, is results matter more than inputs. It's great to know the VOA information, the base stocks, etc. But the REAL data is gleaned from the UOAs!
Napa's syn oils do just fine, as do most others on the market. If you can find them on sale, they are quite a good performer for the group III dollar you spend.