The article says, if I'm not mistaken, that the heat source must be between 1900 and 2400 degrees (Celcius), and I would bet that Vantablack loses its blackness at such temperatures?
Wikipedia indicates the melting point of vantablack being 3000C. I would think a black coloring is pretty heat resistant. It looks like it needs to be 500-750C to create it as well
In vacuum, maybe. Vantablack is made of carbon nanotubes, and those oxidize away in atmosphere above 750C.