Back when I was working on formulating standard liquid foundations, we tested all of them for SPF, to see if we could make any claims. Most of the regular coverage formulas had a SPF of 2, the others were zero. All tinted moisturizers tested were zero. High coverage formulas and concealers got about a 4. The SPF results correlated well with the TiO2 levels - iron oxide levels had virtually no contribution to SPF at all.
Perry and Dr. Bob both have a good point. Since even mentioning anywhere that your SPF coverage had anything to do with iron oxides could result in the FDA forcing a recall of your product, why would you bother?