For plotters, just get a pen with UV ink. Is a UV printer something more fancy?

Those are two completely different things. Nothing to do with UV fluorescent inks. UV printers use special inks which are cured by UV light instead of relying on solvent evaporation like most inks. A bit similar to UV cured resins used by SLA printers or UV cured glues. This makes it easier to print on various materials like metal, glass, and ceramics. UV printing can be done in multiple layers to add 3d texture or using bottom white layer as primer thus providing better colors regardless of base material color.