I think the bond is polar because the electronegativities are much different. The sulfur atom in Sulfur Hexafluoride (like in Sulfuric Acid) has six bonds. That is only possible when the electrons are pulled away. Note that there is no H6S, only H2S, because hydrogen does not pull away the electrons and the octet becomes completed at H2S. As SF6 exists (and it does not stop at SF2), it suggests that fluorine pulls electrons from sulfur.
Furthermore, SF6 is has a high global warming potential. Greenhouse gases have a vibrating dipole moment when the molecule vibrates. This is also the case for Carbon Dioxide and Methane. If SF6 has a potential vibrating dipole moment, the bonds must be polar.
This is only a conclusion simple theory. And I only considered SF6 in the analysis. I do not have hard proof for the statement.
A more funny thing to ask is "What happens at the F-O (or even a Cl-O) bond? Can we 'oxidize' oxygen to an oxidation number of +2?"